Astronomy 3130/5110 Observatory Handbook

Transcript

Astronomy 3130/5110 Observatory Handbook University of Virginia 2011 Contents 1 The 1. 2. 3. 4. McCormick and Fan Mountain Observatories The Leander McCormick Observatory . . . . . . . . . . . . . . . . The Fan Mountain Observatory . . . . . . . . . . . . . . . . . . . Public Night at the McCormick and Fan Mountain Observatories Department of Astronomy, University of Virginia . . . . . . . . . . . . . 1 3 4 5 5 2 The 1. 2. 3. Observatory Calendar and Schedule General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reserving an Observatory . . . . . . . . . . . . . . . . . . . . . . . . . . . . Changing or Deleting the Reservations . . . . . . . . . . . . . . . . . . . . . 7 9 9 10 . . . . . . . . . . . . . . . . . . . . 3 Loss and Breakage, Key, and Safety Agreements 11 4 The 1. 2. 3. 4. Doghouse Observatory 6-inch Clark Refractor Introduction . . . . . . . . . . . . . . . . . . . . . . . Operation of the 6-inch Clark Refractor . . . . . . . . Finding Objects . . . . . . . . . . . . . . . . . . . . . Closing Down . . . . . . . . . . . . . . . . . . . . . . 4.1. Stow the 6-inch Clark refractor . . . . . . . . 4.2. Secure the doghouse . . . . . . . . . . . . . . 4.3. Observer’s Room (Room 106) . . . . . . . . . 4.4. Secure the Observatory and Grounds: . . . . . 5 The 1. 2. 3. Doghouse Observatory 10-inch Meade LX200 Introduction . . . . . . . . . . . . . . . . . . . . . . Operation of the 10-Inch Meade Telescope . . . . . Closing Down . . . . . . . . . . . . . . . . . . . . . 3.1. Stow the 10-inch Meade . . . . . . . . . . . 3.2. Secure the doghouse . . . . . . . . . . . . . 3.3. Observer’s Room (Room 106) . . . . . . . . 3.4. Secure the Observatory and Grounds: . . . . 6 The 1. 2. 3. 4. McCormick Observatory 26-inch A Tour of the Telescope . . . . . . . Opening Procedure . . . . . . . . . . Locating an Object . . . . . . . . . . Telescope Tailpiece . . . . . . . . . . i Clark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 19 19 21 24 24 24 24 25 Schmidt-Cassegrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 29 29 32 32 32 32 32 . . . . 35 38 40 43 45 . . . . . . . . . . . . . . . . Refractor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. 6. 7. 8. 9. 10. Visual Observations . . . Basic CCD Observations Warnings and Additional Closing Down . . . . . . Opening Checklist . . . Closing Checklist . . . . . . . . . . . . . . . . . . Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 48 49 50 53 53 7 The 1. 2. 3. 4. 5. 6. 7. Fan Mountain Observatory 40-inch Astrometric Reflector Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Startup Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . Initializing the Coordinates . . . . . . . . . . . . . . . . . . . . . Shutdown Procedure . . . . . . . . . . . . . . . . . . . . . . . . . The Filter Control System . . . . . . . . . . . . . . . . . . . . . . The Telescope AutoGuider . . . . . . . . . . . . . . . . . . . . . . 7.1. Setup Procedure . . . . . . . . . . . . . . . . . . . . . . . 7.2. Internal Filter Wheel . . . . . . . . . . . . . . . . . . . . . 7.3. Image Procedure . . . . . . . . . . . . . . . . . . . . . . . 7.4. Focus and Finding Procedure . . . . . . . . . . . . . . . . 7.5. Calibrate Procedure . . . . . . . . . . . . . . . . . . . . . 7.6. Track Procedure . . . . . . . . . . . . . . . . . . . . . . . 7.7. Monitor Procedure . . . . . . . . . . . . . . . . . . . . . . 7.8. Many More Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 57 58 58 61 61 62 63 66 66 66 66 67 67 67 67 8 The 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Fan Mountain Observatory 31-inch Tinsley Reflector General Information . . . . . . . . . . . . . . . . . . . . . . Care of the Telescope . . . . . . . . . . . . . . . . . . . . . . Opening Up . . . . . . . . . . . . . . . . . . . . . . . . . . . The Control Room . . . . . . . . . . . . . . . . . . . . . . . Closing Down . . . . . . . . . . . . . . . . . . . . . . . . . . The Control Paddle . . . . . . . . . . . . . . . . . . . . . . . The Guide Box . . . . . . . . . . . . . . . . . . . . . . . . . Alcove and Circuit Breakers . . . . . . . . . . . . . . . . . . Equipment used with 31-inch telescope . . . . . . . . . . . . Log Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 71 73 73 74 76 77 78 79 80 81 9 The 1. 2. 3. 4. Fan Mountain Observatory 10-inch Astrograph General Information . . . . . . . . . . . . . . . . . . Opening procedure . . . . . . . . . . . . . . . . . . . Telescope Operation . . . . . . . . . . . . . . . . . . Closing Down . . . . . . . . . . . . . . . . . . . . . . . . . . 83 85 85 85 86 10 The 1. 2. 3. GenI CCD Camera (Imaging) System Description . . . . . . . . . CCD Camera Specifications . . . . The Dewar . . . . . . . . . . . . . . 3.1. Description . . . . . . . . . 3.2. Normal Operation . . . . . . . . . . 87 89 89 91 91 91 . . . . . ii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Potential Problems and the Dewar Vacuum Operating the CCD Camera . . . . . . . . . . . . . 4.1. Login . . . . . . . . . . . . . . . . . . . . . . 4.2. Starting IRAF . . . . . . . . . . . . . . . . . 4.3. Starting the Voodoo Program . . . . . . . . 4.4. Filter Control System . . . . . . . . . . . . . 4.5. Scope Control System . . . . . . . . . . . . 4.6. Taking an Exposure . . . . . . . . . . . . . 4.7. Ending a CCD Session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 . 93 . 93 . 94 . 94 . 99 . 100 . 102 . 102 GenII CCD Camera (Spectroscopy) System Description . . . . . . . . . . . . . . . . . . CCD Camera Specifications . . . . . . . . . . . . . The Dewar . . . . . . . . . . . . . . . . . . . . . . . 3.1. Description . . . . . . . . . . . . . . . . . . 3.2. Normal Operation . . . . . . . . . . . . . . 3.3. Potential Problems and the Dewar Vacuum Operating the CCD Camera . . . . . . . . . . . . . 4.1. Login . . . . . . . . . . . . . . . . . . . . . . 4.2. Starting IRAF . . . . . . . . . . . . . . . . . 4.3. Starting the Voodoo Program . . . . . . . . 4.4. Scope Control System . . . . . . . . . . . . 4.5. Taking an Exposure . . . . . . . . . . . . . 4.6. Ending a CCD Session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 105 105 107 107 107 108 109 109 110 110 116 117 117 12 The Fan Observatory Bench Optical Spectrograph (FOBOS) 1. Instrument Overview . . . . . . . . . . . . . . . . . . . . . . . . 1.1. The Focal Plane Module . . . . . . . . . . . . . . . . . . 1.2. The Fiber Train . . . . . . . . . . . . . . . . . . . . . . . 1.3. The Bench Spectrograph . . . . . . . . . . . . . . . . . . 2. Available Configurations . . . . . . . . . . . . . . . . . . . . . . 3. Setting Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Filling the Dewar . . . . . . . . . . . . . . . . . . . . . . 3.2. Enabling the Vibration Isolator . . . . . . . . . . . . . . 3.3. Preparing the Spectrograph Room . . . . . . . . . . . . 3.4. Computer Start-up . . . . . . . . . . . . . . . . . . . . . 3.5. Preparing the Dome Room . . . . . . . . . . . . . . . . . 3.6. Please please please... . . . . . . . . . . . . . . . . . . . . 4. Observing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. What Data Should You Collect? . . . . . . . . . . . . . . 4.2. Spectrograph Control System . . . . . . . . . . . . . . . 4.3. Software Initialization . . . . . . . . . . . . . . . . . . . 4.4. Calibration Lamp Exposures . . . . . . . . . . . . . . . . 4.5. Telescope Coordinate Initialization . . . . . . . . . . . . 4.6. Focal Plane Module Focus . . . . . . . . . . . . . . . . . 4.7. Coarse Acquisition . . . . . . . . . . . . . . . . . . . . . 4.8. Fine Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 122 122 124 124 126 127 128 128 129 129 130 131 131 131 133 133 134 135 136 136 137 4. 11 The 1. 2. 3. 4. iii 5. 6. 7. 8. 4.9. Guiding . . . . . . . . . . . . . . . . . . . . . . 4.10. Throughput and Exposure times . . . . . . . . Shutting Down . . . . . . . . . . . . . . . . . . . . . . 5.1. Disabling the Vibration Isolator . . . . . . . . . 5.2. Spectrograph Room . . . . . . . . . . . . . . . . 5.3. Dome Room . . . . . . . . . . . . . . . . . . . . 5.4. Control Room . . . . . . . . . . . . . . . . . . . Troubleshooting . . . . . . . . . . . . . . . . . . . . . . Data Reduction . . . . . . . . . . . . . . . . . . . . . . Neon/Argon/Xenon Spectral Line Identification Charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 138 139 139 139 139 140 140 141 143 13 The Santa Barbara Instruments ST-8/ST-1001E CCD Cameras 147 1. CCD Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 2. CCD Operation with CCDOPS . . . . . . . . . . . . . . . . . . . . . . . . . 151 14 The OptoMechanics Model 10C Spectrograph 1. General Information . . . . . . . . . . . . . . . 2. Use of the Spectrograph . . . . . . . . . . . . . 2.1. Instrument Design . . . . . . . . . . . . 2.2. Spectrograph Set Up . . . . . . . . . . . 2.3. Spectrograph Operation . . . . . . . . . 2.4. Slit and Grating . . . . . . . . . . . . . . 2.5. Camera Rotation . . . . . . . . . . . . . 2.6. Spectral Range . . . . . . . . . . . . . . 2.7. Focusing the Spectrograph . . . . . . . . 2.8. Observing with the Spectrograph . . . . 3. Reduction of Spectrographic Data . . . . . . . . 3.1. Preparation . . . . . . . . . . . . . . . . 3.2. MaxIM DL . . . . . . . . . . . . . . . . 3.3. MIRA . . . . . . . . . . . . . . . . . . . 4. Ne–Hg/Ar Comparison Sources . . . . . . . . . 5. Central Wavelength vs. Grating Tilt . . . . . . 6. References on CCD Imaging and Spectroscopy . 7. File Transfer to UNIX Workstations . . . . . . . 8. Reduction of Spectrographic Data with IRAF . 8.1. Viewing and Extracting Spectra . . . . . 8.2. Setup . . . . . . . . . . . . . . . . . . . 8.3. Usage . . . . . . . . . . . . . . . . . . . 8.4. Extracting the Comparison Spectrum . . 8.5. Wavelength Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 157 157 157 161 163 163 163 163 165 166 167 167 168 168 169 170 171 171 172 172 172 174 176 177 15 The Astrovid 2000 Video Camera 1. General Information . . . . . . . . . . . . . . . . . . 2. Setting Up the Camera . . . . . . . . . . . . . . . . . 2.1. Mounting the Camera . . . . . . . . . . . . . 2.2. Connecting the control box and power supply 2.3. Adjusting the Focus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 183 184 184 185 185 iv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. 4. 5. 6. 7. Setting Up a Video Output Device . . . . . . . . . Camera Controls . . . . . . . . . . . . . . . . . . . Centering the Image on the CCD . . . . . . . . . . Capturing Images With the McCormick Laptop PC Shutting Down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 187 187 188 190 16 The Astronomy Library and Astronomical Literature 1. The Astronomy Library . . . . . . . . . . . . . . . . . . . . . . 1.1. Reference and Information Services . . . . . . . . . . . . 2. Guide to Astronomical Literature . . . . . . . . . . . . . . . . . 2.1. General Guides . . . . . . . . . . . . . . . . . . . . . . . 2.2. The Age of the Computer . . . . . . . . . . . . . . . . . 2.3. Periodicals/Journals . . . . . . . . . . . . . . . . . . . . 2.4. Conference Proceedings . . . . . . . . . . . . . . . . . . 2.5. Observatory Reports . . . . . . . . . . . . . . . . . . . . 2.6. Review Literature . . . . . . . . . . . . . . . . . . . . . . 2.7. Abstracts . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8. Almanacs, Data Books, Handbooks . . . . . . . . . . . . 2.9. Charts and Atlases . . . . . . . . . . . . . . . . . . . . . 2.10. Catalogs . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11. Publisher’s Series . . . . . . . . . . . . . . . . . . . . . . 2.12. Observational Astronomy . . . . . . . . . . . . . . . . . 2.13. Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . 2.14. Specific References Related to Observational Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 193 193 194 194 194 195 196 196 197 197 197 198 199 199 200 201 201 . . . . . . . . . . . . . . 205 207 207 209 211 212 212 214 215 216 216 218 221 221 222 A Using IRAF on a UNIX Workstation 1. Starting IRAF . . . . . . . . . . . . . . . . . . . . . . . . 2. FITS vs. IRAF format . . . . . . . . . . . . . . . . . . . 3. Common IRAF Tasks . . . . . . . . . . . . . . . . . . . . 4. Image Reduction in IRAF . . . . . . . . . . . . . . . . . 4.1. Procedural Overview . . . . . . . . . . . . . . . . 4.2. The CCDRED Package . . . . . . . . . . . . . . . 4.3. CCDLIST—What do I got? . . . . . . . . . . . . 4.4. Test Images . . . . . . . . . . . . . . . . . . . . . 4.5. The Log File . . . . . . . . . . . . . . . . . . . . 4.6. Trimming the Image and Correcting the Overscan 4.7. Bias Combining and Subtracting . . . . . . . . . 4.8. Dark Combining and Subtraction . . . . . . . . . 4.9. Flat-Fielding . . . . . . . . . . . . . . . . . . . . 4.10. Illumination Correction . . . . . . . . . . . . . . . v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Chapter 1 The McCormick and Fan Mountain Observatories 1 2 McCormick and Fan Mountain Observatories (Rev. August 09, 2011) 1. The Leander McCormick Observatory The Leander McCormick Observatory is located on Mount Jefferson at the edge of the University of Virginia Grounds. It is found at latitude 38◦ 02′ 00′′ and longitude 78◦ 31′ 24′′ . The observatory is 866 ft (264 m) above sea level. This observatory has three telescopes which are described briefly below. Other details are given in this handbook. 1. 26-inch Clark refractor: The 26-inch telescope has a 26-inch diameter lens with a focal length of 32.5 ft (9.9 m). Its field of view is about 0.75 of a degree with photographic plates. This telescope has been used primarily for astrometric observations and the observatory plate file contains over 140,000 plates which were taken between 1914 and 1995 for the purpose of determining stellar motions and distances. 2. 6-inch Clark refractor: The 6-inch telescope is an Alvan Clark refractor with a focal length of 1.83m. It is housed in a small roll-off roof observatory (the Doghouse) on the grounds of McCormick Observatory next to the 26-inch dome. 3. 10-inch Meade: The 10-inch telescope is a Meade LX200 Schmidt-Cassegrain telescope with a focal length of 2.5m. It is housed in the Doghouse next to the 26-inch dome. 4. Observatory Building: This building contains a small museum, lecture room, observer’s room, plate vault, restroom, and other support facilities for the observatory. 3 2. The Fan Mountain Observatory The Fan Mountain Observatory is on Mount Oliver in the Fan Mountains; latitude 37◦ 52′ 41′′ , longitude 78◦ 41′ 34′′ . Fan Mt. is 1825 feet (556 m) above sea level and 1200 feet above the surrounding terrain. The observatory is located near Covesville, VA about 16 miles south of Charlottesville. The turn-off from Rt. 29 is about 13.5 miles south of I 64. From Rt. 29 there is a 3.5 mile gravel road to the top. See map. Please exercise care when crossing the railroad tracks as the line is often used by fast moving freight trains and there is no signal. Always come to a complete stop before crossing the tracks. The road to the Observatory is narrow and winding and to avoid traffic jams on the Fan Mountain Public Night, the road will be up only from 7:15–9:00 p.m., and down after 9:15 p.m. only. Warm clothing should be worn for trips to Fan Mt. since it may be much colder and windier on the Mountain than in town and you will be outside (or in the dome) much of the time. Fan Mountain Observatory has three telescopes which are described briefly below. Other details are given in this handbook. 1. 40-inch astrometric reflector: The 40-inch telescope has a 43-inch diameter primary mirror, a 20-inch diameter secondary mirror, and a 40-inch diameter corrector lens to provide a stable, large-field telescope for precise measurements of the motions and distances of nearby stars. It has also been used for studies of galaxies and quasars. Its field of view is about 0.67 of a degree (somewhat larger than the full moon) with 10inch photographic plates. The field of view using the SITe 2048 CCD is approximately 12.5 arcmin on a side. It is also equipped with a fiber-fed low resolution spectrograph system, used to study the motions and metal abundances of giant stars in the Galactic halo. 2. 31-inch Tinsley reflector: The 31-inch telescope is a standard Cassegrain reflector with a 31-inch primary mirror and an 8.5-inch secondary mirror. It is primarily used for near infra-red astronomy.. 4 3. 10-inch astrograph: The astrograph is a wide-field camera for photographing large sections of the sky at one time. Over 900 red-dwarf stars have been discovered with this instrument. 4. Station House: This building contains a darkroom, mechanical shop, restrooms, living quarters, and other support facilities for the Observatory. 3. Public Night at the McCormick and Fan Mountain Observatories McCormick Observatory is open to the public the first and third Friday of each month. No tickets or reservations are necessary. Groups must make special arrangements. Twice a year there is a public night at Fan Mountain, once in April, and again in October. Tickets (which are free) are required for the Fan Mountain Public Night. Call 924-7494 for details. 4. Department of Astronomy, University of Virginia The McCormick and Fan Mountain Observatories are operated by the faculty and staff of the Department of Astronomy at the University of Virginia. For general information about the Astronomy Department, you may consult the World Wide Web URL address of the department’s home page: http://www.astro.virginia.edu. 5 Figure 1. Directions to Fan Mountain Figure 2. Layout of Fan Mountain Observatory 6 Chapter 2 The Observatory Calendar and Schedule 7 8 The Observatory Calendar and Schedule (Rev. August 09, 2011) 1. General Information Both the McCormick and Fan Mountain observatories are now reserved through an online web calendar. The Calendars are used to schedule events and observing runs. There is a calendar for each of the observatories which is found at: http://www.astro.virginia.edu/research/observatories/calendar/ Authorized users may reserve time at either McCormick or Fan Mountain. See Ricky Patterson or the webmaster for information on how to reserve either observatory To browse the calendar, use the McCormick Calendar and the Fan Mountain Calendar links. To reserve the observatory, use the Reserve Observatory link. 2. Reserving an Observatory Before reserving an observatory (referred to as Adding an event on the observatories calendar page), you should make sure that the observatory is available during the times you intend to use it. This can be checked easily by using the list view option on the calendar page for the specific observatory. You need to login to be able to reserve any of the observatories. Contact the course TA to know your group’s login id and the password. You can change your password at any time on the login page. Once logged into the calendar, choose the link add event. At the following page, you need to fill in the following fields: • Start Date: The date of the observation. • End Date: The date when you finish the observation. Note that if you intend to observe till or past midnight, this date is the next day’s date. • Start Time • End Time: Note: midnight is 12:00 AM. • Telescope Use: Enter the details of the telescopes and the equipment you will be using for the observing run. 9 • Category: Use ASTR3130 or ASTR5110 as the category. Enter your group number and the name of the TA. After filling in all the above fields, use the Submit event link to reserve the observatory. If there is a problem with the form, it will take you to a page showing the problem. Correct that and submit the page again. Once you submit an event correctly, it will show you the details of the event added. Make sure the information there is correct. If not, use the Edit this event button to change the event and submit it again. 3. Changing or Deleting the Reservations If you later want to cancel or update your reservation, you need to login into the calendar again and first find that event using the search events link. At this page you can limit your searches by different criteria, such as the start and end dates, instrument use, etc. One of the most useful limiting criterion for you would be to search within your events (use the check-box corresponding to My events), which will display only your events. Once you find your event, use the Edit event link to either update or delete the event. Note: Do NOT reserve the observatories for times/days you don’t need. The telescopes are heavily used and you should give others (including your fellow ASTR3130 or ASTR5110 students) equitable chance for observing. The following applies to ASTR 3130 students only: To insure that a single group does not take up all the observatory time, the following policy will be followed: The observatories calendar will not let any group sign-up for more than two hours of observatory time each night. A group can, however sign up for more hours for a particular night under the following circumstances: • More time is available (check at the observatory calendar) • You are signing up less than 24 hours in advance (this allows every group reasonable opportunity to plan ahead and reserve time). 10 Chapter 3 Loss and Breakage, Key, and Safety Agreements 11 12 Loss & Breakage, Key and Safety Agreements (Rev. August 06, 2007) Loss and Breakage Agreement The equipment you will use in this course is fragile, expensive and very difficult to replace. In order that everyone has equal opportunity to complete the course requirements and responsibility can be assigned fairly we have implemented the following loss and breakage agreement. 1. You are on your honor to report all damage to the instructor or TA immediately. Do not attempt to fix it yourself. Shut down the equipment and report the problem. If the nature of the damage endangers other equipment (roof won’t close, electrical problems) you must contact us. If neither the instructor nor the TA can be reached, contact any astronomy department member. 2. A written description of any damage or problem is to be given to the instructor the following day. In order for observing equipment to be repaired promptly, we must know specifics about the problem. Damage caused by the student will be assessed against you. 3. In the case of loss or damage which cannot be assigned as the responsibility of a given individual, all students authorized to use the equipment during the time period in which the problem occurred will share equally the cost of replacement or repair. Checks on the equipment will be made daily and the last users will be held responsible for its condition. If an item appears damaged or is missing when you first check it out, notify your instructor in writing and the previous users will be assessed damages. 4. Always fill out the observing log for every observing session. No credit will be given for observations carried out during an unlogged session!!! 5. In all cases the judgment of the Astronomy Department in assessing the damage costs is final. We will make every effort to be fair subject to the constraint that the costs must be paid. Normal wear will be allowed for. 6. All assessed costs must be paid within 4 weeks of notification. Your grade will be withheld until all payments have been made. Key Agreement For completion of the requirements of this course you will be issued one or more keys which you must return at the end of the semester. Any keys signed out over night should be returned promptly the next weekday morning. 13 Your grade will be withheld until all keys are returned to the department. These keys are loaned to you for use in completing the requirements of this course. They are not to be copied, loaned to friends, or used to gain access to the department’s facilities for any non astronomy related purpose. You may not bring friends with you to the observatories. Safety Agreement This is a laboratory course and like any lab course there are potential hazards which could result in injury. For the most part you will be working in the dark either outdoors conducting observations or in the darkroom. Use common sense when moving about; do not make any sudden, quick movements. Telescopes have sharp corners and parts that stick out. Make a mental note of the locations of all equipment, including steps or ladders. This information may help you to prevent accidents. In any event, always carry a flashlight. Remember that you are more likely to hurt yourself than large pieces of equipment. McCormick Observatory Much of your observational work will be done here using the 6-inch and 10-inch telescopes in the Doghouse and the 26-inch in the main dome. Some safety notes: 1. The photometer has a high voltage power supply and all the telescopes have electrical connections. Be alert. 2. No horseplay. No alcoholic beverages. No smoking. 3. Watch your footing in the Doghouse. 4. First-Aid equipment is located in the built-in bookshelves in the Observers Room. There are several phones in the building. Note their locations. In case of an emergency, you must dial a “9” before 911: 9-911. Fan Mountain Any trips to the Fan Mountain Observatory will be supervised by the TA or faculty. It is always about 10 degrees colder at Fan, so you will need to dress warmly. Injuries If an injury of any kind occurs, notify the instructor if he or she is present. If the injury is minor and no supervisor is present, you should notify the instructors the next day. If the injury appears even remotely serious call the rescue squad (911). Notify the instructor immediately. (Call her/him at home if necessary.) Emergency numbers are posted by the phone. Wear suitable clothing at all times. Remember than even 60 degree weather can be chilling if you are engaged in observing with a minimum of movement. Metal surfaces get very cold; numbed hands can lead to accidents. Walk slowly and carefully when leaving a lighted room and entering the dark. It takes a minimum of 5 minutes for your eyes to adjust to darkness and more than a half hour for full adaptation. Once your eyes are night adapted, it is best to keep them that way until all observations are completed. Repeated switching from light to dark will cause eye strain. After reading these agreements, sign the pledge. 14 OBSERVATIONAL ASTRONOMY Sign and return this sheet to the instructor of this course. LOSS AND BREAKAGE AGREEMENT I understand the loss and damage policy described elsewhere and agree to promptly pay replacement or repair charges assessed me by the Astronomy Department. I will report all problems in the manner prescribed as quickly as possible. Name: SAFETY AGREEMENT I understand the policy regarding safety for this course and will act responsibly to prevent accidents. Name: KEY AGREEMENT On my honor as a student I agree to return those keys loaned to me upon completion of the course. I will not duplicate any key nor will I loan a key to anyone under any circumstances. Name: ID#: Date: 15 16 Chapter 4 The Doghouse Observatory 6-inch Clark Refractor 17 18 6-inch Clark Refractor (Rev. August 09, 2011) 1. Introduction The 6-inch Clark refractor is housed in the Doghouse at the McCormick Observatory. It has an equatorial mount and is equipped with a Saegmuller weight-driven mechanical clock drive. It is a simple and reliable telescope to use if the proper care is exercised. It is also an irreplaceable piece of equipment; treating it with care will allow it to be used for many, many years to come. The Doghouse telescopes should not be used until you have been shown how to use these telescopes and have been given permission by a TA or faculty member to use them on your own (i.e., checked out). 2. Operation of the 6-inch Clark Refractor Roof: The roll-off roof is operated manually with the winch beside the door. There is a vice clamp holding the chain in place which must be loosened before opening the roof. Be sure to reclamp the chain TIGHTLY after closing up for the night. Never move the roof unless both telescopes are horizontal and clear of its path. Lens caps: Carefully remove lens caps on both the 6-inch lens (1, see Figures) and finder (4) after opening the roof. Always replace them before closing. Be aware that they have a tendency to bind. Clock Drive: Start and stop the clock drive with the push-pull control (6) on the north side of the pier on the outside of the clock mechanism cover. Open the glass door on the west side of the pier and you will find the winding shaft (7), for the crank. The crank is 19 kept on the shelf with the eyepiece box. Open the access door on the south side of the pier so you can watch the pulley and weight. Slide the crank sleeve over the shaft and slowly wind the weight up until the top of the weight is level with the bottom of the access hatch in the hollow pier. Never overwind the drive; this will damage the drive mechanism. You will have to rewind it every 45 minutes or so. If the drive is operating properly, the governor (5) inside the door will spin rapidly. Always turn the drive off before leaving the building. Finder: A low-power, wide-field finder telescope (4) is mounted piggyback on the 6-inch. It contains cross-hairs which are somewhat difficult to see against a dark sky. The alignment between the two telescopes may not be perfect—i.e., an object centered on the cross-hairs may not be in the center of the main telescope field, so always start with the lowest power eyepiece. The focus may need to be adjusted. Do this by carefully moving the draw tube either in or out. However, be careful not to knock the finder out of alignment while doing this. Controls: Apart from the clock drive there are only 5 controls. The clamps and slow motion controls (8), are located at the ends of the long shafts extending back toward the eyepiece end of the telescope. The two outer knobs control RA slow motion and clamp, and the inner ones have the same functions in DEC. The focus is on the side of the eyepiece mounting tube. Clamps: The clamps are the larger pair of barrel shaped knobs. If turned counter-clockwise, they completely free the Right Ascension (RA) and Declination (DEC) motions for pointing the telescope. When the desired object has been located, carefully clamp first one then the other, by turning the knobs clockwise. These only need to be firm not tight. Do not over-tighten them, as they become difficult to undo and may damage the gears. Clamping the RA engages the clock drive, if it is “on”, and causes the telescope to track the object across the sky. Do not attempt to move the telescope without making sure the appropriate motion is unclamped. Slow motion: The slow motions are the flatter, disk-like knobs, again one for each motion. Turning these knobs adjusts the pointing of the telescope in either RA or DEC for centering objects in the eyepiece field, correcting the drive motion, etc. The telescope must be clamped in that motion, in order for these to function. The DEC slow motion moves the telescope on a tangent arm which has limited travel. Be sure that the tangent arm is in the middle of its travel range, before you begin observing. Focus: Use the focus knob on the side of the eyepiece mount to adjust the eyepiece focus. After changing eyepieces the image may need refocusing. It is difficult or impossible to focus on faint or diffuse objects, so use a bright, naked-eye star before trying to find such an object or use a nearby field star. Occasionally you will have to adjust the sliding draw tubes to find a focus. A diagonal prism is provided to allow easier viewing through the eyepiece. Setting Circles: The setting circles (2) are the large white wheels marked with coordinates; one in DEC and one in Hour Angle (HA). The HA wheel is marked from 0 - 24 hours in roman numerals, and measures the time since the last meridian crossing. Therefore, depending on the telescope orientation, 0 hour angle (i.e. the meridian position) will correspond to either 20 Figure 1. 6-inch Alvin Clark Refractor. (1) Objective Lens, (2) Setting Circles, (4) Finder, (8) Slow Motions and Clamps, (9) Eyepiece. 0 hours or 12 hours. Larger numbers are toward the west. E.g. an Hour Angle of 3 12 hours east would be found at XX 12 on one side of the pier and VIII 21 on the other. A little care and practice will prevent confusion. The coordinates on the painted wheel surfaces are reasonably accurate for declination. For HA, it is best to use those inscribed in brass on the edge of the wheel. These must be read with the mounted magnifiers (3). Eyepieces: Eyepieces are stored in the eyepiece box on the shelf in the corner of the Doghouse. Most objects are best viewed under low or moderate power, rather than high power which is recommended only for high surface-brightness objects such as planets and double stars. Replace the eyepieces in the eyepiece box before leaving. 3. Finding Objects A list of interesting objects is available on the table in the Doghouse. Coordinates may be found in Norton’s Star Atlas. When searching for objects, always use the lowest power eyepiece (i.e. longest focal length) first. There are three basic ways to find objects: 1. By eye: Using Norton’s, or any other source, point the telescope at the appropriate region of the sky and search for the object with the finder. This will probably not work for fainter objects, but is suitable for the most interesting objects. 21 Figure 2. 6-inch Alvin Clark Refractor. (2) Setting Circles, (3) Setting Circle Magnifiers, (5) Drive Governor, (6) Drive Push-Pull Switch, (7) Drive Winding Shaft, (8) Slow Motions and Clamps, (9) Eyepiece. 2. By DEC: Carefully set and clamp the telescope at the DEC of the object as accurately as possible. Find the approximate location in the sky, and leaving the HA unclamped, search in the finder while moving the telescope slowly in HA. The finder is small, so fainter objects will be rather dim. Check out likely candidates in the main telescope. Small adjustments in DEC may be necessary. 3. By DEC and RA: Set the telescope to the DEC of the object and clamp. Then calculate the hour angle from the general relation HA = ST − RA where HA is the hour angle, ST is the sidereal time, and RA is the right ascension of the desired object. If the HA is negative, the object is east of the meridian. Add 24 hours to the HA and set the telescope to the resulting HA. If the HA is positive then set the telescope to the HA directly. (NOTE: This is the procedure for the 6-inch refractor. The 10-inch HA dial goes in the opposite sense; a negative HA is west of the meridian instead of east. The strategy is the same however so just keep in mind how the dials are divided.) Determine the ST from the sidereal clock. (Alternatively set your watch to the ST using the table provided in Norton’s, or from the sidereal clock in the 26-inch dome. Over a few hours, your watch will keep sufficiently accurate sidereal time for this method.) Once the coordinates are set and the drive turned on, you may search for the object at your leisure. You will probably have to search around a bit in the finder. Practice the method on bright stars first. It sometimes helps to repeat the procedure, or at least double-check the setting circles if you can’t find what you’re looking for. If objects seem consistently and substantially offset in HA, the sidereal time may be wrong. 22 While observing, you may need to make small corrections with the slow motions for errors in the clock drive. It is best not to touch the telescope otherwise during observations. At any given time, you will not be able to reach all of the listed objects. Usually, you can observe any object whose HA is less than 3 hours. The farther north the object, the greater the hour angle to which you can observe it. Note that the cardinal directions in the finder and main telescope will be inverted relative to their orientation in the sky. 23 4. Closing Down 4.1. Stow the 6-inch Clark refractor • Park the Clark with the tube level and on the west side of the pier, with the objective pointing south. Clamp telescope in RA and Dec. • TURN OFF DRIVE. Wind drive, stopping when the top of the weight reaches the bottom of the access hatch. Never overwind the drive. • Cover main and finderscope objectives. Replace eyepiece tube cover. • Stow all eyepieces (close the box). • Make sure you have logged your use of the telescope in 6-inch logbook. 4.2. Secure the doghouse • Clean up table and shelves. Take all trash with you. Return all borrowed material. Stow CCD/computer, etc., in observer’s room in main building. • Unlock roof crank and roll roof shut, making sure it clears telescopes. Lock roof crank tightly, with roof rolled firmly to its limit. • Turn off (inside and outside) lights. Shut door, making sure it is locked. 4.3. Observer’s Room (Room 106) • Record use of telescope (along with your name, and the number of visitors) in log book kept in observer’s room. This is not a trouble log. • Make sure table in observer’s room is clean when you leave. • If you have logged in, be sure to log out of the workstation (leander). Power off the monitor. • Report ANY problems with telescope by email to: [email protected] Additionally, immediate, serious problems must also be reported to the TA or Ricky Patterson (214-0414 lives in Vyssotsky Cottage, can help at night, but be sure to leave a message if there is no answer) or Ed Murphy (293-5634, can help at night). 24 4.4. Secure the Observatory and Grounds: • When leaving, turn on switches for security lights in closets (Room 102 and 104A). • Leave door to Room 102 (closet) slightly open to control humidity. • Turn off manually controlled light switches (museum display cases, light boxes, dome and foyer). • Make sure that inner main door LOCKS behind you when leaving, and close outer main doors. • Close the gate. Please Note: The gate should be closed at night at ALL times EXCEPT during a Public Night, Group Night or Telescope Observing Night. bf It should be closed while you are observing at the telescope, and only opened long enough for you to drive through. • Contact someone IMMEDIATELY if you are unable to stow the telescope SAFELY. 25 26 Chapter 5 The Doghouse Observatory 10-inch Meade LX200 Schmidt-Cassegrain 27 28 10-inch Meade LX200 Schmidt-Cassegrain (Rev. August 09, 2011) 1. Introduction The 10-inch telescope is a Meade LX200 Schmidt-Cassegrain and is found in the Doghouse next to the 6-inch refractor (see Chapter 3). The Schmidt-Cassegrain is equatorially mounted and is driven by an electric clock drive, and its motion can be operated from a hand-held control paddle. The Doghouse telescopes should not be used until you have been shown how to use these telescopes and have been given permission by a TA or faculty member to use them on your own (i.e., checked out). 2. Operation of the 10-Inch Meade Telescope 1. Roof: The roll-off roof of the Doghouse is operated manually with the crank beside the door. There is a vice clamp holding the chain in place which must be loosened before opening the roof. Be sure to reclamp the chain tightly after closing up for the night. Never move the roof unless both telescopes are horizontal and clear of its path. Refer to the Open/Close Checklist for the Doghouse Observatory (Chapter 3). 2. Objective Cover: Remove objective cover carefully. Be careful of the corrector plate just beneath as there is no handle on the cover. Be sure to replace it when you are finished observing. 3. Telescope Power: Turn on the power strip located at the base of the pier on the lower east side of the pier. Then, place the ON/OFF switch located in the upper right corner of the power panel (11) to the ON position. The telescope should now be receiving power. 29 4. Declination Clamp: Loosen the declination clamp. This clamp is a palm sized knob with a grooved edge located in the center of an aluminum ring on the outside of one of the fork arms. Loosen the clamp by turning the knob counterclockwise. Once the clamp has been loosened, move the telescope to 0◦ declination by aligning the 0 on the declination setting circle (3) with the declination pointer (4) on the fork. Tighten the declination clamp. 5. Paddle and Drive: The paddle controls the slow motions and the drive. Use the direction keys on the control paddle (12) to slew the telescope in the east-west direction until the right ascension pointer (9) is at zero hour angle. This is accomplished by aligning the right ascension pointer (9) with the hour angle pointer (16) located just above the center of the power panel on the drive base. Note that the telescope has variable slew rates: slew, find, center, and guide corresponding to the buttons on the keypad with the numbers 7, 4, 1, and 0 respectively. An abbreviation for each slew rate is written above the corresponding number on each button. Simply press the appropriate button to change to the desired slew rate. 6. Star Alignment: The celestial coordinates must now be set by aligning the telescope with two reference stars. At this point the menu on the control paddle should read: → TELESCOPE OBJECT LIBRARY Make sure that the arrow is pointing to the TELESCOPE option and press the key marked ENTER. The menu should now read: → 1) SITE 2) ALIGN Press the NEXT key to move the arrow down to the ALIGN option and then press ENTER. The menu should now read: → 1) ALTAZ 2) POLAR Make sure that the arrow is pointing to the ALTAZ option and press ENTER. If the menu DOES NOT change, but the checkmark on the right of the menu moves to ALTAZ, press ENTER again. The menu should now read: 1 Star or 2 Star Alignment Press the key with the number 2 on it to select Star Alignment. You will now be asked to pick two stars from a list contained in the telescope’s computer. The computer will then ask you to center these two stars in turn in order to set the coordinates for the telescope. The menu should now read: 30 Level base, then press ENTER The base has already been levelled so go ahead a press ENTER. The menu now reads: Press ENTER, pick align star 1 Press ENTER to get a listing of the stars available in the computer’s memory. Use the NEXT and PREV keys to move the arrow to the star of your choice. Once you have found the star that you wish to use, press ENTER. The menu will then read: Center Starname then press ENTER Use the control paddle to slew the telescope to the star that you have chosen and center the star in the field of view. DO NOT LOOSEN ANY CLAMPS OR MOVE THE TELESCOPE BY HAND. This will cause the computer to lose track of where it is in the coordinate system. Once the star is centered press ENTER. The menu will then ask you to go through the procedure of picking and centering a star once more. Press ENTER, pick a second align star just as before, USE A DIFFERENT STAR THIS TIME, center the star, and then press ENTER. The computer should now be oriented and happy. The menu on the control paddle should have returned to the first option: → TELESCOPE OBJECT LIBRARY 7. Locate Messier Object: The telescope can now be easily moved to any Messier object by pressing the key which has an M for Messier above a number 9 on it to obtain: M object: Key in the Messier number of the object that you wish to find and press ENTER. The menu now displays some information about the object such as its magnitude, what type of object it is, etc... Press GOTO and the telescope will automatically slew to the object. Use the control paddle to center the object in the field of view. 8. Locate NGC Object: You can just as easily find objects whose NGC number you know by pressing the key marked with CNGC above the number 3. 9. Eyepieces: Eyepieces are stored in the eyepiece box on the shelf in the corner of the Doghouse. Most objects are best viewed under low or moderate power, rather than high power which is recommended for high surface-brightness objects such as planets and double stars. Replace the eyepieces in the eyepiece box before leaving. 31 3. Closing Down 3.1. Stow the 10-inch Meade • Park the Meade on the meridian, with the tube pointed to zenith. • Clamp the telescope, turn off power. Hang control paddle from silver handle on south side of the end of the tube. Don’t hang control paddle elsewhere. • Stow all eyepieces (close the box). Replace eyepiece tube cover. • Make sure you have logged your use of the telescope in 10-inch logbook. 3.2. Secure the doghouse • Clean up table and shelves. Take all trash with you. Return all borrowed material. Stow CCD/computer, etc., in observer’s room in main building. • Unlock roof crank and roll roof shut, making sure it clears telescopes. Lock roof crank tightly, with roof rolled firmly to its limit. • Turn off (inside and outside) lights. Shut door, making sure it is locked. 3.3. Observer’s Room (Room 106) • Record use of telescope (along with your name, and the number of visitors) in log book kept in observer’s room. This is not a trouble log. • Make sure table in observer’s room is clean when you leave. • If you have logged in, be sure to log out of the workstation (leander). Power off the monitor. • Report ANY problems with telescope by email to: [email protected] Additionally, immediate, serious problems must also be reported to the TA or Ricky Patterson (214-0414 lives in Vyssotsky Cottage, can help at night, but be sure to leave a message if there is no answer) or Ed Murphy (293-5634, can help at night). 3.4. Secure the Observatory and Grounds: • When leaving, turn on switches for security lights in closets (Room 102 and 104A). • Leave door to Room 102 (closet) slightly open to control humidity. • Turn off manually controlled light switches (museum display cases, light boxes, dome and foyer). 32 • Make sure that inner main door LOCKS behind you when leaving, and close outer main doors. • Close the gate. Please Note: The gate should be closed at night at ALL times EXCEPT during a Public Night, Group Night or Telescope Observing Night. It should be closed while you are observing at the telescope, and only opened long enough for you to drive through. • Contact someone IMMEDIATELY if you are unable to stow the telescope SAFELY. Those are the basics. To learn more about all of the fancy features on the telescope consult the LX200 manual located in the Doghouse or in the TA filing cabinets. 33 Figure 1. Meade LX200 Schmidt Cassegrain Telescope 34 Chapter 6 The McCormick Observatory 26-inch Clark Refractor 35 36 The 26-inch Clark Refractor Revised September 2010 The 26-inch refracting telescope was built by Alvan Clark Sons and completed in 1875. It is housed in the dome on Mount Jefferson; the observatory was completed in 1884, and dedicated on April 13th, 1885. The Clark refractor has a 26-inch diameter lens with a focal length of 32.5 ft (9.9 m). Its field of view is about 0.75 of a degree with photographic plates. This telescope has been used primarily for astrometric observations and the observatory plate file contains over 140,000 plates which were taken between 1914 and 1995 for the purpose of determining stellar distances and motions. For a full history of the telescope see: http://www.astro.virginia.edu/research/observatories/26inch/ Figure 1: The 26-inch Clark Refractor in proper stow position. 37 1. A Tour of the Telescope The dome is entered via an entrance to your left as you come in the front door of the observatory building. There is an additional entrance located on the south side of the dome, which is not normally used (and should not be used for public access since it requires people to pass by mechanical equipment in the dark). Figure 2: The dome entrance as viewed from inside the dome. The green box indicates the location of the light switches and plug for the dome charger. There are three dome slits which are opened and closed by ropes which hang along the dome wall. There are two floor mats near the entrance which are to collect water from known leaks in the dome slits. The leaking water must be kept off of the original observatory floor. There is no need to move these mats (e.g. the observing chair will move over them), but if they need to be moved, they must be replaced in their original location. There are two observing chairs. The larger of the two runs on a track around the edge of the dome. This track must be clear for the chair to move safely. Damage or injury may result if the track is not clear. Please note that the chair will move freely with the floor mats in place. A smaller chair is located opposite the larger chair. This chair can move freely and the wheels can be locked when in use. Never lock the wheels when stowing the chair at the end of the night. There is a small box which can also be used for observing; care should be exercised, since the box can damage the floor. 38 There are two sets of telescope controls. One is located on the pier and the other on a hand paddle attached to the telescope itself. The sidereal time can be read from a digital clock on the far wall and the local time is read from the analog clock on the pier. Equipment for maintaining and repairing the telescope is stored in the dome at the South end of the pier. This equipment should not be touched or moved. 39 Figure 3: An observer adjusts the location of the telescope from the pier controls. Also highlighted are the locations of local and sidereal clocks in the dome. 2. Opening Procedure 1. Allow at least one hour of preparation time before your planned observations. 2. Turn on the wall switch lights which are to the left of the dome entrance (see green box in Figure 2). Directly adjacent to the switch is a small toggle that will adjust the intensity of the lights. 3. Unplug the dome motor battery charger (hanging cord) from the wall outlet above the light switch, remove the extension cord and place it on the shelf in the alcove to the right of the plug. Never leave this extension cord attached when the dome motor is unplugged. 4. Open the dome shutters by pulling on the appropriate ropes. The dome itself can be moved from both the console and the paddle using the Dome Left or Dome Right toggle (See Figure 4 (2) or Figure 5 (4)). The dome can also be moved from the hanging plug by holding down the left or right buttons. Always allow the dome to come to a complete stop before changing the direction of dome motion. Always inspect the wall of the dome to be sure that no objects will be caught by the dome ropes as the dome rotates. Always use caution when rotating the dome, and watch for any potential problems. Never store objects by leaning them against the wall of the dome. 40 Figure 4: Pier Control Panel 5. Turn on the telescope power from the console (top left button, see Figure 4 (1)). This will activate all console controls, paddle controls and console lights. To do this push the Power On button on the console (note there are also power controls on the top of the hand paddle). The red indicator light on the bottom left will illuminate when the power is on (Figure 4 (3)). 6. To unclamp the Right Ascension (RA) or Declination (Dec) motions, press the RA Clamp and/or Dec Clamp button on the control console (see Figure 4 (4)). This will release the telescope clamps. Red indicator lights will illuminate when the telescope is unclamped (see Figure 4 (4)). To slew the telescope down into position for observing, unclamp the RA Clamp, press the West (W) slew button (see Figure 4 (8)). This will move the objective toward the west and the tailpiece down toward the pier. Releasing the button will stop the motion. Care must be exercised whenever the telescope is being slewed. Make sure that the telescope’s path is clear, and always watch it as it moves. Particular care should be taken with any movements of the tailpiece near the pier. Release the W button to stop slewing once the tailpiece is within easy reach. Again, use caution to avoid hitting the pier, or anything else. Motion in declination works in a similar fashion (although the Dec slew motor does not work consistently). Unclamp the Dec Clamp to allow movement in Declination. 7. To open the lens cover, flip the objective cover toggle down (see Figure 4 (6)). The green indicator light will turn red when the objective is opened. Note: Always open the objective cover before closing the dome shutters. Sometimes paint chips or other materials on the dome slits can fall onto the objective while the 41 dome is in motion or while closing the dome shutters. This can cause serious damage to the objective. 8. To rewind the RA drive sector, press the Sector Reset button on the console or hand paddle (see Figure 4 (7) or Figure 5 (2)). The indicator light will turn red as this drive is reset. When the light turns off then the drive is reset and the observer has about 1.5 hours of motion available before needing to reset. 9. To turn on the clock drive, press toggle the Track switch on either the console or hand paddle (See Figure 4 (5) or Figure 5 (5)). The indicator light will turn red when the tracking is on. Figure 5: Hand Paddle Control Panel 42 3. Locating an Object 1. Pick the object that you want to observe. Note: Any declination greater than 24 degrees will cause the telescope to hit the pier soon after the object passes the meridian. Although it may not appear obvious from ground level, the declination periscope (brass tube) will hit the shelf on the top of the pier starting at +24 degrees even though the tailpiece will clear the pier. Amount of Time after Transit before Telescope Hits Pier Declination Time (minutes) +23:40 Will Pass +24:00 19 +25:00 18 +26:00 10 +27:00 8 +30:00 6 +34:00 6 +35:00 6 +40:00 5 +45:00 6 +50:00 9 +55:00 9 +60:00 10 +65:00 12 +70:00 21 +75:00 34 2. Set the declination. The current declination of the telescope can be read off of the declination periscope on the side of the telescope opposite the finding scope. Gently move or slew the telescope to the correct declination. Clamp the telescope in declination while holding the telescope in place with the silver metal bar around the tailpiece. Never push against the tailpiece itself. After clamping small adjustments can be made with the slew buttons. While clamping the telescope will move slightly. 3. Set the Hour Angle (HA). Compute the HA: HA = Sidereal Time RA (A positive value indicates minutes to the west, negative indicates minutes east, i.e., if the RA is greater than the sidereal time the object is east of the meridian.) Read the hour angle from the large circle on the polar axis (1 division = 5 minutes). Clamp the telescope in Right Ascension. 43 4. Position the dome with an open slit over the objective lens. Declination Coverage of the Dome Slits when Placed Along the Meridian Shutter Top Middle Bottom To South To North +6 to +45 +35 to +73 -24 to +14 +67 to pole -18 to Horizon 5. Use the track toggle to initiate the clock drive. The tracking only functions when the telescope is clamped in RA. 6. Center the object of in interest in the finder scope. Compare the star field through the finder with your finding charts. Center your object on the cross hairs using the fine adjust slew motions on the paddle. 7. Clamp the telescope in RA. Tracking will commence as soon as the telescope is clamped in RA. Periodically check the finder to ensure that the object has not drifted out of view. 44 4. Telescope Tailpiece The telescope tailpiece has been designed to allow for simultaneous use of the eyepiece, Astrovid 2000 camera, and an SBIG CCD. Flip mirrors located at the back end of the telescope allow one to change between instruments. The tailpiece uses the 2 inch eyepieces found in the metal cabinet in the Observer’s Room. We currently have three eyepieces for use on the 26-inch. Great care should be exercised in handling all of the eyepieces and filters. Available Eyepieces: 1. 20 mm Nagler Type 2 (great for use with planets!) 2. 35 mm Panoptic 3. a 55 mm Pl¨ossl Figure 6: Left: Eyepieces for the 26-inch are located in the metal instrument cabinet in the Observer’s Room. 45 Right: The backend of the telescope with major features boxed in red. The metal bar around the tailpiece is used to move the telescope. The declination periscope is located on the opposite side of the telescope from the finder scope. 46 5. Visual Observations Visual observations are conducted using a set of 2-inch eyepieces kept in the Observer’s Room (See Figure 6). 1. Loosen the screws on the eyepiece holder on the back end of the telescope and remove the stop, storing it on the desktop. Slide in the desired eyepiece and tighten the screws to lock in the eyepiece. Stow both the eyepiece cap and the stop on the desktop for the remainder of the night. 2. The rough focus for the backend can be turned with the crank on the pier table. A rough guide to where the focus has been historically is located 45 degrees counter clockwise from the location of the rough focus. Return the focus crank to the pier table. 3. Fine focus knobs are located on the eyepiece holder on the backend of the telescope (see Figure 6). 4. Make observations! 5. When finished, remove the eyepiece and return it to the case. Replace the stop. Then, follow the close down procedures in Section VIII. 47 6. Basic CCD Observations 1. Carefully roll the PC cart from the observer’s room into the dome. 2. The powerstrip on the PC cart can be plugged into the outlet on East side of the pier. 3. Connect the male end of the ribbon cable into the parallel port on the PC. Connect the female end of the ribbon cable to the parallel port on the CCD Head. 4. Connect the 5-pin power cable from the CCD power supply to the CCD head. Plug the power supply into the power bar on the telescope. If everything is connected properly then, the unit now has power. The red LED on the head of the CCD head will glow and the fan will being spinning. 5. Plug the PC and the PC monitor into the power strip on the PC cart. Start the PC by pressing the power button. 6. Insert/Check the filter. The filter is mounted in a holder just before the instrument. A set of BVR filters are stored in the Observers Room. 7. The rough focus for the back end can be turned with the crank on the pier table. A rough guide to where the focus has been historically is located 45 degrees counter clockwise from the location of the rough focus. Return the focus crank to the pier table. Fine focus knobs are located on the backend of the telescope. 8. Center the object of interest in the eyepiece as described in Section III. 9. Fine focus for the CCD camera is located on a knob near where the CCD attaches to the tailpiece. 10. Flip the mirror to send the light into the instrument. 11. Image the Object. A PC is required to control the CCD. The CCD is controlled by the Maxim DL software, which operates in the Windows environment. 48 7. Warnings and Additional Instructions 1. Do not leave the telescope unattended with the drive running. If leaving the dome for any length of time close down the telescope. 2. The sector is located behind the Right Ascension drive. For historical reasons (the original drive was a weight driven governor clock drive, with a weight that had to be reset every 90 minutes), the main gear for the RA drive is only a small section of a full circle. This will drive the telescope for about 1.5 hours, after which the sector must be reset. You are advised to reset the sector 3. Remember that the 26-inch can not point to all places in the sky. The telescope is always on the West side of the pier, never on the East. This means that you should try to observe objects before they transit, especially northern ones. You will have to be mindful in your observing plans in order to ensure you can observe the desired objects within these limitations. 4. The Observer’s Room contains the Astronomical Almanac, Norton’s Star Atlas and the SAO Catalog. The computer in the Observer’s Room is connected to the department’s network. The 26-inch observing logbook is also located here. Please do not forget to fill out the log when you observe. 5. There is a phone on the east side of the pier and a phone in the Observer’s Room. There is a list of departmental phone numbers on the wall in the Observer’s Room as well as a list of the emergency contacts. 6. There is a First-Aid kit in the Observer’s Room in the built in bookshelf. 7. There are pressurized water fire extinguishers in the entry hall and the lecture room. These should not be used on electrical or chemical fires. A small extinguisher for all types of fires is located downstairs in the room outside of the bathroom. Call 911 (9-911 from a University phone) before attempting to put out the fire by yourself. 49 8. Closing Down 1. Turn off the RA Drive and reset the sector. The reset is complete with the red indicator light turns off (see Figure 4 (7) or Figure 5 (2)). 2. Close the objective cover using the console (see Figure 4 (6)). The indicator light will turn green when the cover is completely closed. Note: Always close the objective cover before closing the dome shutters. Sometimes paint chips or other materials on the dome slits can fall onto the objective while the dome is in motion or while closing the dome shutters. This can cause serious damage to the objective. 3. The telescope stow position is: +38 degrees declination and HA of 4 hours east. Bring the telescope down so that the objective cover points at the zenith. The telescope tube should be parallel to the pier. Then, use the RA slew to move the telescope 4 hours east. If you are unable to safely stow the telescope, call for help immediately. 4. Clamp the telescope in RA and Dec. The red indicator lights will turn off when the telescope is clamped (see Figure 4 (4)). If using the CCD, shut down the CCD before turning of telescope power. 5. In general, green indicator lights mean that it is okay to leave the telescope and the dome (except for the on red light which simply indicates that the power is on). Red indicator lights mean that some aspect of the telescope is not in the proper mode for telescope storage. If the objective cover light is green and no other indicator lights are illuminated aside from the red power light, then turn off power to the telescope with the button on the pier. The red indicator light will turn off when the power is turned off (see Figure 4 (1)). 6. Close the dome shutters completely. Close the shutters by using the ropes. Often the shutters will stick when very close to being closed. Be sure to give a strong hard tug to make sure the shutters are completely closed. You must visually inspect the dome shutters to ensure they are completely closed. The dome shutters will make a sound even when they are not completely closed, thus only hearing the shutters close is not enough to confirm they are closed. 7. Rotate the dome so that the charger cord is hanging just to the right of the outlet. Plug in the extension cord, and plug in the dome charger (See Figure 2). 8. Clean up the area before leaving. Be sure to return all objects to their proper storage locations. (1) Carefully push the large observing chair past the second window on the left side of the room. Return the small observing chair to the west side of the room against the track and next to the historic tailpiece jack. Do not lock the wheels when stowing the 50 small chair. Make sure the box is against the pier, being careful to not damage the floor. (2) Return ladders or any other equipment to its location against the pier. (3) Ensure that the focus crank is on the desktop on the north side of the pier. (4) Return all reference materials to their proper locations in the Observer’s Room. (5) Return the computer and other equipment to their proper locations in the Observer’s Room. (6) Return the eyepieces to the closet (stowed in their case). 9. Turn off lights in the dome and close the door to the dome. 10. Observer’s Room: (1) Record use of the telescope in the log. Please record ONLY your name, purpose of telescope use (e.g. Astr3130) and the number of visitors. (2) Log out of the computer in the observer’s room and return books and other equipment to its proper place. Turn off the monitor. (3) Report any and all problems to: [email protected] Immediate, serious problems must also be reported to the TA or Ricky Patterson (214-0414; lives in Vyssotsky Cottage beside the observatory; available at night) or Ed Murphy (293-5634; available at night). The TA is your first access point for help. If you are unable to reach either TA, then contact your professor or another faculty member at the department. Phones are located both in the dome and in the Observer’s Room. In the Observer’s Room is a list of phone numbers for members of the Astronomy department. It is critical that problems be reported in a timely manner. 11. Secure the observatory and grounds. (1) Lights in most of the observatory are on motion sensors and will turn themselves off after you leave. It may seem disconcerting to leave the observatory with lights on, but do not turn off the motion sensors; the next person who arrives after dark will thank you! Lights in the dome room and entrance are not on motion sensors. Be sure to turn off these lights when leaving. (2) Leave the door to the Observer’s Room open and leave the door to the closet (with the security light switches) slightly ajar to control humidity. (3) Turn on the outdoor security lights in the closet. (4) Make sure the inner door locks behind you as you leave. (5) Close the outer doors. Make sure that the left-hand outer door is bolted. If you close both doors without bolting the left-hand door, it can be very difficult to open the doors. 51 (6) Close the gate. The gate should be closed at all times (at night) except during public events (e.g. public night). It should be closed while you are observing at the telescope, and should only be opened when driving in or out. Never leave it open for someone who is due at any minute; they will have to open and close the gate for themselves). 52 9. Opening Checklist 1. Turn on Lights. 2. Open Dome Slits. Unplug Dome Charger and stow extension cord. 3. Turn on telescope power and drive. 4. Unclamp the telescope, slew it so the tailpiece is accessible, reset the sector. 5. Open the objective cover. 6. Turn off main lights, prepare to observe. 10. Closing Checklist 1. Turn off the RA drive. Reset the sector. 2. Close the Objective Cover. 3. Stow the telescope at +38 degrees, and HA = 4 hrs east. Clamp the telescope in both RA and DEC. 4. If using the CCD, turn off power to the CCD. Turn off power to telescope. 5. Close the dome shutters completely, visually inspecting the slits. Do not rely on the feel of resistance on the dome pulley rope as an indication that the slit is completely closed. 6. Align the dome correctly and plug in the dome motor. 7. Clean up the area before leaving. Be sure to return all equipment to its proper storage location within the dome or Observer’s Room. 8. Turn off light in the dome. Close the door to the dome. 9. Sign the log book and clean up the Observer’s Room. 10. Secure the Observatory and Grounds. Be sure that the security lights are on at the observatory, the observatory is locked and that the gate is closed. 11. Contact someone immediately if you are unable to stow the telescope safely. Report all problems to [email protected] 53 54 Chapter 7 The Fan Mountain Observatory 40-inch Astrometric Reflector 55 56 The Fan Mountain 40-inch Telescope (Rev. August 15, 2011) 1. Introduction Figure 1. The Fan Mountain 40-inch Telescope. This manual gives general instructions for operating the Fan Mountain 40-inch telescope, the filter control system, and the autoguider. Fan Mountain Observatory is a research facility of the University of Virginia Department of Astronomy. The instruments are being used for graduate student teaching and the research programs of faculty and their students. You should conduct your work with the utmost care, patience, and forethought, keeping in mind that the equipment is delicate, complex, and expensive to maintain. To minimize the potential for accidents, you should have a clear idea of your observing plan for the night, including the optimal observing times of your target and calibration objects, lists of coordinates and finder charts, and an efficient plan for minimal changing of filters. Do not neglect to obtain the necessary set of bias frames and flat fields for calibration, or the rest of your data will be worthless. If anything in this manual is unclear, consult the TA or appropriate faculty member for clarification. As with all delicate equipment, NEVER force any moving part beyond reasonable 57 and expected resistance. Always keep track of the telescope position in relation to the sky, dome, and objects within the dome. NEVER touch any optical element. Oils from your skin will permanently embed into glass surfaces and optical coatings. It is better to leave small amounts of dust on optical surfaces than to risk scratching or marring them with attempts at cleaning. If dust is a serious problem, ask the TA, Jim Barr, Charles Lam, or a faculty member to remove it with dry nitrogen. If, while in the control room, you hear any peculiar noises or have any uncertainty about the location of the telescope or dome, you should make the trek up one flight of stairs to check the dome in person. If you are uncertain about any aspect of operating the telescope, or any other piece of instrumentation, STOP and ask someone. THINK BEFORE DOING. Home phone numbers: Fan Mountain caretaker Nick Nichols (979-0684), David McDavid (434-985-4378), Jim Barr (540-832-5304), Steve Majewski (434-975-6435). In case of emergency don’t hesitate to call, but please try not to call unless it is absolutely necessary. 2. Description The Fan Mountain 40-inch telescope has an f/13.5 Schmidt-Cassegrain optical system with a 40-in (1-m) aperture, a focal plane image scale of 15.3′′ mm−1 , and a corrected photographic field of 50′ . It has a computerized telescope control system (TCS) developed by DFM Engineering, Inc. and described in detail in the TCS486 Operations Manual on the bookshelf in the control room. A pair of fans inside the telescope tube near the corrector plate can be turned on with the toggle switch on the west side of the telescope tailpiece. Power to the toggle switch is on only when the CCD switch on the bottom rack panel (Fig. 2) in the control room is on. Running these fans helps to improve tube seeing under some conditions. 3. Startup Procedure 1. Begin filling out a new log form in the blue Observing Log notebook which is kept on the bookshelf in the control room. 2. The CCD switch on the Rack Panel (Fig. 2) controls a large uninterruptible power supply (UPS) and is normally left ON all the time. If it is not already on, turn it on and leave it on. 3. Power up the autoguider PC if it is not already on. It will boot to a Windows 7 logon prompt. Turn on the telescope control PC (the one in the electronics rack on the far right side of the table). It will boot to a DOS prompt. This PC shares the large monitor and keyboard in the middle of the table with the autoguider PC (which must be powered up first) through a pushbutton toggle switch with LEDs indicating which system is selected. 58 Figure 2. The Rack Panel. 4. At the telescope control PC DOS prompt, enter tcs to start up the DFM Telescope Control System. Set the date and the universal time, referring to the clock in the electronics rack for the local time. To do this: • Start from the Main Menu (press ESC if it is not displayed) • Enter 1 (Initialization Menu) • Enter 1 (Set date and time) • Fill in the blanks with the date and UT • The TCS will assume the telescope is pointed at the zenith and will approximately initialize the coordinates based on the latitude, longitude and local sidereal time. 5. Set the switches on the DFM panel (Fig. 3) to Track, Track Off, Drives Off, Auto Dome Off, External Computer On, and Dome Home, then turn on the Motor Drive Chassis, Motors On, and Drives switches. Figure 3. The DFM Panel. 6. At the telescope control PC DOS prompt, enter tcs to start up the DFM Telescope Control System. Set the date and universal time, referring to the clock in the electronics rack for the local time. (Start from the Main Menu (press ESC if it is not displayed), 59 enter 1 (Initialization menu), enter 1 (Set date and time), then fill in the blanks.) The TCS will assume the telescope is pointed at the zenith and will approximately initialize the coordinates based on the latitude, longitude, and local sidereal time. 7. Upstairs in the dome, use the ladder to connect the shutter power cord from the electrical outlet to the shutter motor box and turn the knob on the motor box counterclockwise. The shutter will open and automatically stop when it is done. Unplug the power cord from the motor box. If you don’t, you’ll destroy the cord or the connectors when the dome moves and you will be in serious trouble when you need to close the dome. 8. Turn on the TCS monitor on the desk in the dome. This monitor and keyboard will function even when the shared monitor and keyboard in the control room are being used by the autoguider PC. Adjust the brightness and contrast as desired. When working in the control room and taking data, you will usually want to have this screen dim. 9. Use the control paddle (Fig. 4) to slew the telescope to the North (towards the horizon in the direction of the desk in the dome room) just far enough so you can reach and remove the telescope lens cover by climbing up the ladder to the upper level. Strap the lens cover to its stand on the upper level so the wind won’t blow it away. DFM Engineering In Focus Out Slew N W Set E S L R Dome Figure 4. The Dome, Focus, and Telescope Control Paddle. 10. Horizon Limit: You may find that you have passed the TCS horizon safety limit in slewing the telescope to the North to get to the lens cover, and the telescope will no longer move by motor control. If this happens, go back to the control room, turn off the Drives and Motors On switches on the DFM panel, then go back to the dome and push up on the telescope tube by hand while standing on the upper platform to move it in declination until it points well above the horizon. Then go back to the control room and turn the Motors On and Drives switches back on. For the safety of the telescope, go back to the dome and use the paddle to verify that normal motor operation is restored. 11. Use the paddle to slew the telescope back to the zenith. 60 12. With the dome slit facing South (AZIMUTH 180.0), which is the HOME position, turn on the Dome Track and Auto Dome switches on the DFM control panel so the dome will automatically follow the telescope. 13. In the TCS Main Menu enter 4 (Miscellaneous menu), enter 1 (Set switches), then turn on RATE CORRECTION, which will enable automatic track rate correction derived from the mount model parameters currently compiled into TCS, and DOME, which must be consistent with the setting of the Auto Dome switch on the DFM control panel. 14. In the TCS Main Menu enter 3 (Rates Menu), enter 1 (Set Track Rates), then input 14.980 for the RA rate and leave the rest of the fields blank. Press Enter for the changes to take effect. 15. Turn on the Track switch on the DFM control panel to start the telescope tracking. 4. Initializing the Coordinates 1. For the safety of the telescope, always do this operation in the dome. 2. Pick a star near the zenith from the BRIGHT STAR LIST in the Astronomical Almanac. In the TCS Main Menu enter 2 (Movement menu), enter 1 (Set slew position), then enter the coordinates and their associated equinox. When TCS asks “Any Changes?” respond with a RETURN. 3. In TCS, enter 7 (Start slew). Be prepared to stop the telescope if it should wander off to extreme angles. You can do that by entering 8 (Stop slew). 4. Center the star in the finder scope eyepiece, assuming it is aligned with the main scope. If you aren’t sure you have the right star, check it in Norton’s Star Atlas on the desk in the dome. 5. From the TCS Main Menu, enter 1 (Initialization menu), enter 2 (Set telescope position), then enter once again the coordinates and equinox for the star you just centered. This will update the telescope position in TCS to the correct coordinates. 6. To set the TCS coordinate display to any desired equinox, start from the Main Menu, enter 4 (Miscellaneous menu), enter 2 (Set display equinox), then enter a decimal year. 5. Shutdown Procedure 1. Set the DFM panel switch to Dome Home to send the dome to the home position (AZIMUTH 180.0). Wait for the dome to go home, then switch Auto Dome Off. 2. Using the paddle, point the telescope low to the North over the upper dome platform and replace the lens cover. 61 3. Plug in the shutter power cord, and turn the knob clockwise to close the shutter. Unplug the power cord from the motor box after the shutter has closed. 4. Turn off the DFM Panel Track switch, then slew the telescope to the zenith with the paddle. 5. Turn off the Drives, Motors, and Motor Drive Chassis switches on the DFM Panel. 6. Do NOT turn off the CCD switch on the Rack Panel. Leave it on. 7. Turn off the telescope control PC power switch. 8. Finish filling out the Observing Log notebook and return it to the bookshelf in the control room. 6. The Filter Control System The filter wheels inside the telescope tailpiece above the CCD camera shutter can be operated from the filter control panel on the south face of the tailpiece when the switches are set to LOCAL or from a computer in the control room when the switches are set to REMOTE. When used with the GenI CCD camera the filter wheels can also be operated from the camera control program through a popup window, and filter information is recorded automatically in the image FITS headers (see documentation for the GenI camera). Filter wheel A (the lower one, also known as filter wheel 1) has 4 openings spaced at 90◦ intervals and holds 6-in square filters. Filter wheel B (the upper one, also known as filter wheel 2) has 6 openings spaced at 60◦ intervals and holds 4-in square filters. To load a filter into a filter wheel, first open the filter wheel access door (the rectangular panel above the filter control panel held shut by clamps) so you can see the filter wheels inside the tailpiece. Switch the filter wheel to LOCAL and use the SLEW button on the filter control panel to rotate it. Open the lock at the edge of the filter opening you select, slide the filter into the slot, then close and gently screw down the lock with your fingers. The filter opening in the telescope light path is the one diametrically opposite the one at the access door. 1. To control the filter wheels remotely, begin by turning on the filter PC (white tower) underneath the table in the control room. It shares the monitor and keyboard in the middle of the table with the autoguider PC through a splitter switch. The filter PC boots to a DOS prompt. 2. Enter cd c700\motion at the DOS prompt to get to the correct directory. If the default filters.txt file does not correspond to your arrangement of filters in the filter wheels, make a new file in the same format which does. Then enter motion to start the filter control program. Ignore error messages about No blank found. 62 3. When the program asks Hit Return when wheels are homed?, go upstairs to the dome and HOME both filter wheels under LOCAL control if you have not already done so. Then switch both wheels back to REMOTE and go back down to the control room. 4. Now enter a RETURN in response to the Hit Return when wheels are homed? prompt on the filter PC. Enter ? to get a list of commands. The command goto filtername should place the filter you specify in front of the detector. Experiment with issuing commands and going upstairs to verify the actual filter wheel positions until you are sure the system is set up correctly. 5. After this point, if you move the filter wheel under LOCAL control and wish to go back to REMOTE, exit and restart the motion program on the filter PC as described earlier. Otherwise the program may not indicate correctly which filter is in the beam at any time. Available filters include standard 4-in square UBVRI and 6-in square Washington filter sets, a 4-in square H-alpha/red continuum interference filter pair, 4-in square H-beta, OIII, NII, and SII interference filters, and a small collection of other assorted interference filters, including a DDO51 filter. The filters are stored away from moisture, dust, and extremes of temperature in wooden boxes on the table below the bookshelf in the control room and should be kept there except for periods of active use when conditions are not potentially harmful. Filter observations can be calibrated with observations of Landolt standard stars listed in the catalog on the bookshelf in the control room. See other references on the bookshelf for details of the filter characteristics, instructions on using IRAF to reduce CCD photometry data, and methods for the transformation of CCD photometry data to standard systems. Some useful references are: • Landolt, A. U. 1992, AJ, 104, 340 (standard star catalog including finder charts) • IRAF Photometry Documentation (see http://iraf.noao.edu/docs/photom.html) • Sung, H., & Bessell, M. S. 2000, PASA, 17, 244 7. The Telescope AutoGuider Almost all research facility telescopes are equipped with an auxiliary autoguider, a device that assists the main telescope in tracking a target for a longer time than the telescope alone is capable of. The 40-inch Fan Mountain telescope can track a star unaided for approximately 3 minutes (when pointed within ≈ 20◦ of the zenith). With the autoguider, exposures of up to 30 min have been tested, and longer ones are possible. The autoguider was built during the summer of 2001 by Jim Barr, Jeff Crane, Charles Lam, Eugene Lauria, and Kiriaki Xilouris. 63 Figure 5. The Autoguider mounted on the 40-inch. The autoguider consists of a CCD video camera (SBIG STV) connected to an 8-inch Meade LX Schmidt-Cassegrain telescope that is mounted on the main telescope tube, supported by a pivot stage. This structure enables limited but independent motion of the Meade with respect to the main telescope tube, increasing the possibility of finding a guide star close to the target area. Between the Meade and the STV there is a focal reducer to optimize the image scale for autoguiding and a JMI motorized focusing stage to enable remote focusing of the guider from the control room. The manual focus knob on the Meade telescope has been disabled and should not be used. Characteristics of the autoguider system are given in Table 1. The autoguider can be controlled from its controller box, which is mounted on the west side of the telescope tailpiece, or remotely from the control room using the autoguider PC and the SBIG STVRemote application software. The pivot and the focusing stages are normally operated from the control room. A special cable is available to operate them from the dome room. Aperture Resolution Limit Focal Length Focal Ratio Image scale STV pixel size STV pixel scale STV Field of View Table 1. 200 mm 0.69 arcsec 2000 mm (EFL 1190 mm w/focal reducer) f/10 (f/5.95 w/focal reducer) 103 arcsec/mm (173 arcsec/mm w/focal reducer) 7.4 microns (640x480 pix) 0.76 arcsec/pix (1.28 arcsec/pix w/focal reducer) ∼6x8 arcmin (∼10x13 arcmin w/focal reducer) Characteristics of the autoguider system. To operate the Autoguider make sure that: 64 1. There is power to the tailpiece of the telescope. 2. The STV controller box in the dome is turned on. 3. The parallel cable from the camera head is connected to the controller box. 4. The video cable is connected to the controller RCS port marked Video Out via an RCA to BNC adapter and is routed through the dome floor to the control room. 5. The Serial I/O (RS232) cable is connected to the controller and is routed through the dome floor to the control room. 6. The video monitor cube on the computer table in the control room is turned on and is connected to the video cable from the controller box in the dome. 7. The Serial I/O cable from the dome is connected to a serial port of the autoguider PC in the control room. 8. The autoguider PC in the control room has Window 98 up and running. It shares the large monitor and keyboard in the middle of the table with the TCS PC through a splitter switch. Figure 6. The STV virtual control panel window on the autoguider PC. On the autoguider PC click on the STVRemote icon to start the remote control software (See Fig. 6.) You will normally see “Link Established” in the PC Message window as the serial link to the controller box is automatically established. If you do not, you may need to select either COM1 or COM2 (whichever works) from the Link pulldown menu to establish the link. 65 7.1. Setup Procedure Click Setup, then click Parameter to cycle through the Setup menu. Click Value to adjust a parameter. Most of the Setup parameters should be correct by default, but you can easily cycle through the choices and select any options you want. You can dismiss the Setup menu by clicking Setup again. All the buttons on the STV Remote virtual control panel work according to this model. 7.2. Internal Filter Wheel A filter wheel inside the STV camera head allows selection of an R, G, B, or Clear filter to approximate the passband being used by the imager on the main telescope in order to reduce autoguiding error due to differential atmospheric refraction. The filter position is changed from the Setup procedure described above, where it appears as one of the adjustable parameters. Sometimes a commanded change of filter or the function of “Covering the CCD” in Tracking or Calibration mode will stall, but this is easily remedied. Click Setup and advance to “Adj Filter” in the Setup menu sequence by clicking Parameter a few times. If the display reads “Fail”, click Value repeatedly to adjust the displayed voltage until the “Shtr” position is as close as possible to the optimum value of 7.5%. The display will then begin to read “Pass” and the malfunction will be corrected. 7.3. Image Procedure To begin taking images click Image, then click Parameter repeatedly to see the adjustable parameters, then set each one by clicking Value. Choose a likely exposure time (say 5–10 s), set Continuous, then click Image again to start a continuous video stream on the monitor cube. 7.4. Focus and Finding Procedure Focus the 8-inch Meade by pushing the buttons on the focus hand paddle on the control room table while watching the video monitor. You can adjust the focusing speed with the rotary button between the IN and OUT focus buttons. Move the Meade about its zero point position with the small hand paddle on the table to find a star if none appears on the monitor. When you have the 40-inch pointed at an object and are ready to set up for autoguiding, use the same procedures to find a bright guide star and an appropriate exposure time and to adjust the focus for the filter you have selected. 66 7.5. Calibrate Procedure Click Calibrate and set AUTO Mode. Click Calibrate again to start the STV automatically learning how far and in what directions its four relays move the telescope for guiding, by exercising the relays and measuring the resulting displacements of the selected guide star. If the calibration sequence is successful, the Message window will show “Passed” and the monitor cube will display four arrows showing the motions produced by the relays. 7.6. Track Procedure To start tracking click Track, set AUTO Mode, and click Track again. The tracking status will be displayed on the monitor cube and in the Message window. 7.7. Monitor Procedure The Monitor functions include monitoring the seeing, checking the optical quality of the Meade, and measuring the periodic errors in the drives. 7.8. Many More Features If the STV doesn’t behave the way you expect it to, consult the Operating Manual STV for much more detailed information on its operation. You will also find many more functions which are not mentioned here, as well as complete instructions for running the AUTO Mode procedures manually with a great variety of interactive options. 67 68 Chapter 8 The Fan Mountain Observatory 31-inch Tinsley Reflector 69 70 31-inch Tinsley Reflector (Rev. August 06, 2007) 1. General Information The 31-inch (79 cm.) Tinsley reflector is located on Fan Mountain. The telescope is a general use reflector originally used with photomultipliers and a photographic plate specrograph. Currenty extensive hardware upgrades and instrumentation efforts are underway to transform the observatory into a more modern research facility capable of IR imaging and grism spectroscopy. This upgrade and instrument project is funded through an NSF grant. Projects in the upgrade include: a drive system upgrade, a new IR Carmera, and an autoguider. Due to the status of this upgrade project the 31-inch will only be avaialable for public nights, twice a year. For more information about the project or use of the telescope please contact Michael Skrutskie ([email protected]) 71 The 31-inch (79 cm.) Tinsley reflector is located on Fan Mountain. Here is some information about the telescope. Comments 31 inches in diameter, 120-inch focal length, 6.25 inches thick, wt. = 368.8 lbs., the hole is 8.75 inches in diameter. All mirrors are Pyrex. Primary 4X Secondary 8.48 inches in diameter, 1.75 inches thick. System focal length 480 inches. f/16 8X Secondary 5.474 inches in diameter, 0.875 inches thick. System focal length 960 inches. f/32 Plate scale 16.9 arcsec/mm (calculated). Measured value = 16.2 (Zissel) to 17.5 (Rosenberg) arcsec/mm. Limiting visual magnitude Dome Estimated at approximately 16 mag. on the best nights. 24 ft. Observa-dome. Finderscope Eyepiece 5” Maksutov 3” finder Black 25 mm. + Xfer system 25 mm. 12.7 mm. 72 Field 30’ 2-3 15’ 2.75’ 6’ 2’ Power 75X 15X 960X 480X 950X 2. Care of the Telescope The telescope should always be stored in a horizontal position in order to prevent the accumulation of moisture on the main mirror. The telescope should not be left unattended for more than a few minutes unless you turn off the drive and either move the slit away from the telescope or close the dome shutters. 3. Opening Up 1. Locate light switches. The red and white lights in the dome room are controlled by rotary dimmer switches to the right of the door as you walk in. 2. Open dome shutter. The dome shutter is opened and closed by plugging in the plug hanging from the right side of the shutter. Plug into the wall outlet and hold switch in direction wanted (open to right, close to left). Letting go of switch will stop the dome shutters. Be careful not to break chain when dome is fully open or closed. The limit switches do not always work. Unplug and hang the cord over the extension arm after the slit is open to prevent the cord from catching on projections as the dome is rotated. 3. Turn on telescope main power switch on the west side of the pier. 4. Open primary mirror covers, remove covers for secondary mirror and finder scopes. The main mirror cover can be removed by simply pulling on the handles on the swing open doors. The doors are held closed by two latches (one at the top and the other at the bottom of the doors when the telescope is horizontal) which will give under pressure. Rotate the small catches into the handles to ensure the doors stay open. The doors must be pushed closed individually, closing the one closest to pier first. The secondary cover is removed by grabbing the handle and rotating the cover until the slots line up with the catches; the cover can then be pulled off. Be careful when removing and replacing the cover and make sure that the slots and the catches are aligned. 73 5. Push set button on control console next to drive rate switches. 6. The RA and DEC. clamps, dome rotation, focus, slow motions, and offset trigger are located on the control box hanging from the telescope. Auxiliary dome rotation controls are located on the panel above the console. 7. The drive is turned on by the switch on the upper left corner of the console. 8. Go to the Control Room 4. The Control Room The telescope is controlled electronically by a computer system which is composed of entirely commercial hardware and software. The hardware and software manuals can be found in the Control Room. Initializing the coordinate readout software: 1. Starting the alignment procedure. (a) Move the cursor to the Telescope option in the menu bar at the top of the screen using the mouse. (b) Press and release the left mouse button. The Telescope menu will appear. (c) Move the cursor to the Link option in the menu. (d) Press and release the left mouse button. The Link menu will appear. (e) Move the cursor to the Establish... option in the menu. (f) Press and release the left mouse button. The ‘Alignment Procedure window will appear on the screen directing you to start step 2. 74 2. North Celestial Pole alignment. (a) Point the telescope at 90 degrees declination (the north celestial pole). (b) Move the cursor to the OK button in the Alignment Procedure window using the mouse. (c) Press and release the left mouse button. The Alignment Procedure window will change directing you to start step 3. 3. First alignment star. (a) Changing the alignment star (optional) Use the menu bar and icons below it to display the desired star on the screen. Use the mouse to place the cursor on the desired star. Press and release the left mouse button. The Object Identification window will appear displaying information about the star and buttons. Move the cursor to the Alignment Star button in the window using the mouse. Press and release the left mouse button. The display will now show the desired star as the alignment star. (b) b) Point the telescope at the alignment star. (c) c) Move the cursor to the OK button in the Alignment Procedure window using the mouse. (d) d) Press and release the left mouse button. The Alignment Procedure window will change, directing you to start step 4. 4. Second alignment star. (a) Changing the alignment star (optional) - See section 3a. (b) Point the telescope at the alignment star. (c) Move the cursor to the OK button in the Alignment Procedure window using the mouse. (d) Press and release the left mouse button. The angular separation that the encoders swept out, the calculated angular separation between the two alignment stars and their difference will be displayed in the Alignment Procedure window. The difference is zero if the alignment is perfect. (e) If the alignment difference is less than five degrees move the cursor to the Accept button in the Alignment Procedure window using the mouse. (f) If the alignment difference is greater than five degrees move the cursor to the Reject button in the Alignment Procedure window using the mouse. Restart the alignment proceedure at step 1. If the difference persists, a hardware problem is the most likely cause. 75 (g) Press and release the left mouse button. The display will use the Night Vision colors and display a bulls-eye indicating where the telescope points on the sky. As you move the telescope the bulls-eye will move accordingly. The telescope now has control over the screen so that the bulls-eye never leaves the screen. 5. Changing the position display. (a) To select a numerical display of the telescope position instead of the default graphical display: Move the cursor to the Telescope option at the top of the screen using the mouse. Press and release the left mouse button. The Telescope menu will appear. Move the cursor to the Digital Setting Circles... option at the bottom of the menu. Press and release the left mouse button. (b) To change back to the graphical display, press and release the left mouse button or space bar on the keyboard. 6. Temporarily regaining manual control of the display. (a) Move the cursor to the telescope icon at the top of the screen and under the menu bar. (b) Press and release the left mouse button. The icon will change, indicating that telescope control of the display has been disabled. (c) To re-enable telescope control, repeat steps A and B. 5. Closing Down 1. Turn off drive. 2. Place the telescope in a horizontal position and cover both primary and secondary mirrors. Make sure both top and bottom catches on the primary doors are fastened and that the secondary cover is completely on. Replace covers on finders. 3. Close dome by rotating the dome until the cord is near a socket. Unhook the cord and plug it in. Make sure slit is completely closed. 4. Fill out log with closing information. 5. Turn off all lights and check that nothing has been left on. 6. Close and lock the door behind you. 76 6. The Control Paddle RA and DEC clamps: These switches unlock the RA and DEC axes. When the lights above the switches are on the axis is unlocked. These switches control locking motors so the lock takes a few moments to act. If the switch is thrown or reversed rapidly, the state of the lock might not change. (Sometimes throwing the switch fails to do anything.) If the axis fails to respond as expected, recycle the switches. When the declination axis is unclamped, the declination slow motion centers (the slow motion is a motor driven offset arm and it can run out of travel). Sometimes, this motor “runs away” and runs the arm to the limit. Such action causes an abnormal noise and should be countered by pressing the reset button. (This can happen spontaneously as well as when the axis is unclamped, and it always happens when the power is turned on.) Focus: This switch racks the secondary in and out in order to focus the telescope. This is connected with the focus readout on the desk. Dome rotation: Rotates the dome. Up is clockwise, down is counter-clockwise. Fast-Slow switch: Sets the slow motion rate to fast or slow at the operators discretion. Up is fast, down is slow. Slow motions: The four buttons actuate the slow motions. The center switch changes the directions of the buttons (the northward dec changes to southward, the westward RA button is now eastward, etc.). If the slow motions balk or act with abnormal noise, 1) check rate and make sure right speed is selected; 2) recycle locks; 3) hit reset; 4) hold button and the motion might straighten out on its own. (This is the last resort.) Spare: Not connected to anything. 77 7. The Guide Box The guide box was designed to provide finding and guiding optics so they would not have to be duplicated on each piece of equipment. To this end the box contains an angled mirror to intercept the light beam. The mirror is controlled by a knob on the left side of the guide box. This knob has three positions: full clockwise, which moves a small hole into position in the middle of the light path; a center position, which completely intercepts the beam with the mirror; and a full counter-clockwise position which intercepts virtually none of the light beam as it moves a large hole into position. The guide box also contains two power panels for powering equipment on the tailpiece. These panels are normally “cold” and have to be plugged in to power to operate. The best place to plug in the panels is the 110V and 6.3V socket on the telescope close to the declination axis. The back left power panel can be plugged in there and the front right panel can be plugged into the back panel. The whole guide box can be rotated into a comfortable position by loosening the single set screw in the base of the telescope. Be careful not to break power cords running from the guide box to sockets elsewhere when rotating the guide box. 78 8. Alcove and Circuit Breakers The alcove of the dome contains the circuit breakers and power supply for telescope, with the exception of the main circuit breaker which is located in the “garage” of the station house. (It is marked “small bldg.” and is #16.) The alcove switch controls the overhead light in the alcove; the outside switch controls the white light just outside the door. The switch marked “station house” controls the bright outside light on the bridge from the station house to the 1 meter dome. Figure 2 gives the layout of the outside wall. The main fuse is on the 220V. line coming into the dome. If any unusual electrical connections seem to be occurring, particularly if the dome will not rotate, it could be due to one side of the 220V line being bad. The power rack in the dome is the power supply for the telescope. Usually any electronics necessary for the instrumentation on the telescope, such as photometers etc., is located in a separate rack. Underneath the desk on the rack is the power supply proper. This contains the on-off switch for the telescope and, on the right side, the rest button for the setting circles. It also contains a switch to reverse the sense of the slow motions depending on which side of the pier the telescope is. Under the power supply is a panel of fuses marked according to function; under this is a panel of indicator lights to indicate the status of the various relays that control motor direction, etc., for the telescope. The heaters and air conditioner in the dome were originally intended to provide a dual service of temperature control and dehumidification. The intent was that the air conditioner would keep the dome cool during the day while the heater would prevent dew from forming. The humidistat should be off while observing. 79 9. Equipment used with 31-inch telescope 1. Single-channel pulse counting photometer 2. Dual-channel photometer 3. The Ridell-Spotz Spectrograph 4. An Eyepiece EQUIPMENT Offset guide plate Black eyepiece plate 1 1/4 inch eyepiece focusing mount Black eyepiece 25 mm eyepiece 12.7 mm eyepiece transfer system 8X secondary 4X secondary FILTERS Stromgren Johnson DDO Hβ w&n Hα w&n SET Set 1 Set 2 Set 3 Set 1 Set 2 λ4166 λ4516 λ4256 Set 1 Set 2 LOCATION Fan Fan Fan Fan Fan Fan Fan Shop on telescope CONDITION poor poor poor u labeled non-standard o.k. o.k. very good very good very good very bad very bad terrible 80 10. Log Procedure All observers are requested to enter the following information in the logbook. Entries are to be made at both opening and closing times. If weather doesn’t allow observing enter as many items as possible. Explanation: On the first line for the night the observers name and equipment are to be entered. The following conventions can be used: photometer 1 = single channel; photometer 2 = dual channel photometer. The next two lines are the opening and closing records, respectively. The following explain the entries. Opening or closing record: 1. Date – month/day/year 2. EST – Eastern Standard Time 3. Temp – Temperature from thermometer 4. Hum – humidity from dome hygrometer 5. Wind – estimated wind speed 6. % clouds – estimate of percent of cloud cover during night 7. Transp – transparency in clearest regions during observations on scale of 0 mag to 5 mag based on apparent magnitude of faintest star visible to naked eye 8. Seeing – estimated mean seeing disk in seconds of arc 9. Hrs. worked – number of hour during which observations were made or attempted 10. Comments – list observing program, problems, or other general remarks you feel appropriate. Problems should also be reported to the proper individuals the next morning, in a trouble log, and/or to email trouble log [email protected]. 81 82 Chapter 9 The Fan Mountain Observatory 10-inch Astrograph 83 84 10-inch Astrograph (Rev. August 06, 2007) 1. General Information The 10-inch Astrograph is located at the Fan Mountain Observatory. It is a wide-field camera for photographing large sections of the sky. Over 900 red dwarf stars have been discovered with this instrument. It is currently (2007) being refurbished by members of the Charlottesville Astronomical Society for a joint project with the Astronomy Department. The following procedures may be outdated by the time you read this. 2. Opening procedure 1. Red and white light switches are to the left of the door as you come in. 2. Open dome by hand. Handles are on the shutters. 3. Uncover 10-inch and the finder. 3. Telescope Operation 1. The switches for the drive and the circle lights are mounted on the declination tangent arm. 2. The hand paddle controls the dome movement and RA (right ascension) guide. 3. Declination guide is manual tangent arm. 4. The telescope is clamped in right ascension and declination by hand wheels. Loosen these wheels and move the telescope by hand. Clamp telescope when you have found your field in the finder. 5. In the box on the middle table, you will find a 32mm Brandon eyepiece which is used for low power with the finder. Also the focusing eyepiece for the 10-inch is kept here. It is a K25mm. 6. Remove the 12.5mm eyepiece and barlow from the 6-inch finder. (Just let it hang from the cord.) Insert the 32mm Brandon eyepiece. This gives about 32 power. (wide field) 85 7. Use the 12.5mm eyepiece and barlow for guiding. This eyepiece has a battery controlled reticle. 8. On the top of the Astrograph, there is a Telarod reflex finder. It projects a 1/2◦ , 2◦ , and 4◦ reticle on the sky. It also is battery operated. 9. Use the K25mm eyepiece with the finding plate located in the tailpiece to locate your region in the Astrograph. Hold the eyepiece base against the glass and scan your field. 10. To focus the Astrograph, hold the K25mm eyepiece against the finding plate and look at a bright star. Focus with the chain wheel. 11. The plate holder is located in the station house darkroom. It is in the second drawer down to the left. 12. Remove the finding plate from the Astrograph and insert the plate holder in its place. The shutter is the dark slide. 4. Closing Down 1. Turn off drive and circle lights. 2. Return finding plate to the tailpiece. 3. Turn of reticle and the telarod reflex sight. 4. Stow the telescope on the east side of the pier parallel to the floor pointing south. 5. Cover the optics, clamp axis. 6. Close the dome and rotate it to the east (left, if you are in the doorway facing the telescope). 7. Fill out the log book and turn off lights. 86 Chapter 10 The GenI CCD Camera (Imaging) 87 88 The GenI CCD Camera System (Imaging) (Rev. August 17, 2011) 1. System Description The GenI CCD system uses the Generation I controller developed by San Diego State University (Leach group) and now managed under the company name of Astronomical Research Cameras, Inc. (ARC). The detector is an SI424A scientific grade CCD imager manufactured by Scientific Imaging Technologies, Inc. (SITe). The SDSU controller is mounted directly on a CCD liquid nitrogen dewar with a serial fiber optic communications link leading from the controller housing to a PCI interface card in a Sun Ultra5 computer. For operation with the GenI controller, the toggle switch on the back panel of the computer should be set to “GEN I”. The power supply for the controller is a box mounted on the east side of the 40-in telescope tailpiece, and the box has a switch which must be turned on for the controller to operate. This power supply is plugged into an AC outlet on the tailpiece which receives power only when the CCD switch on the bottom rack panel in the control room is also turned on. The controller operates an electromechanical shutter mounted inside the tailpiece, either under software control or by way of a toggle switch on a black box near the controller power supply. The Sun Ultra5 control computer is named crux and uses the Sun Solaris2.8 operating system with the CDE window system. The user interface to the CCD controller is the a program called Voodoo developed by SDSU, executed with the command juju, which runs a version of the program which has been modified locally for use with the GenI controller and CCD on the 40-in telescope at Fan Mountain. Images are stored on disk in FITS (*.fits) format and can be transferred from disk to magnetic tape (4mm DAT DDS4). A typical full frame requires 8.6MB of storage. Images can be displayed and analyzed using IRAF tasks. This manual does not explain the details of using IRAF, but IRAF has an extensive built-in help facility, and full documentation is available on the web at the IRAF Project Home Page. 2. CCD Camera Specifications Table 1 summarizes the current configuration of the CCD camera, chip, and dewar Fig. 1 is a plot of quantum efficiency vs. wavelength for the CCD in the GENI camera. 89 Spec Dewar Value IR Labs liquid nitrogen cooled, 1 ℓ capacity heating resistor hold time ∼ 36 hours Chip SITe 2048 × 2048 CCD Imager back-illuminated, thinned to enhance blue response Operating Temp. unstable above −100◦ C optimal operating temperature ∼ −110◦ C lowest achievable temperature ∼ −134◦ C temperature readout may be erratic Format 2048 (cols) × 2049 (rows) 24 µm square pixels Field of View 12.5′ × 12.5′ on FMO 1-m 1 pixel = 0.365′′ CTE 0.99998–0.99999 Dark Current negligible at −110◦ C Full well > 150, 000 electrons/pixel Readout 85 s for full frame (2049 rows × 2088 columns) maximum ADU = 65535 single amplifier readout mode no on-chip binning no subarray capability Low Gain Gain: 3.84 e− /ADU, Readout noise: 8.9 e− High Gain Gain: 2.06 e− /ADU, Readout noise: 16.9 e− Table 1. Current configuration of the CCD chip and camera. 90 Figure 1. Plot of CCD chip quantum efficiency vs. wavelength. The relevant curve for our chip is the top solid curve. 3. The Dewar 3.1. Description The CCD is mounted on a cold finger in an evacuated chamber behind a fused silica window in a liquid nitrogen dewar and is cooled by direct contact of the cold finger with liquid nitrogen. The dewar, manufactured for ARC by Infrared Laboratories, Inc., has a capacity of 1 ℓ and a hold time of about 36 hours. The dewar is capable of cooling the CCD to a temperature as low as about −134◦ C, but normally a heating resistor in the dewar is used to regulate the CCD temperature to some optimal working value between −110◦ and −100◦ C. A small electric fan with a rotary on/off switch is mounted on the tailpiece of the 40-in telescope to blow warm air through a tube to a connector near the top of the CCD dewar to produce a continuous flow across the dewar window to prevent fogging. It should normally be left running constantly while the camera is mounted on the telescope. 3.2. Normal Operation 1. At least 24 hours before your scheduled observing night, send email to Nick Nichols ([email protected]) and ask him to make sure the CCD dewar is filled and the defogging fan is running. Top off the dewar at the beginning of the night, and again at the end of the night as a courtesy to the next observer if observations are scheduled for the following night. 91 2. Filling the dewar takes about 15 minutes if it is still cold from the previous filling, but up to 40 minutes if starting from room temperature in summer. It takes about 4 hours for the dewar to cool from room temperature to the optimal operating temperature of −110◦ C, so it is important to allow sufficient time for the cooldown before observing. You should therefore have the dome and catwalk doors open (in order for the air inside the dome to reach temperature equilibrium with the outside air, which is necessary for good seeing) and the dewar filled before sunset. 3. To fill the dewar, attach the connector at the end of the hose from a 25ℓ LN2 tank to the CCD dewar and fill the dewar with liquid nitrogen until you see liquid spilling out the side vent of the connector. It takes some time for the hose to cool sufficiently to allow nitrogen to pass without evaporating, and the connectors will become coated with frost. When done filling, unscrew, cover, and stow the fill tube and nitrogen tank. Then attach the spill-tube to the CCD dewar. The spill-tube will prevent nitrogen from spilling from the dewar at moderate angles; however, when moving the telescope to large zenith distances such as when the lens cover is removed or replaced or during dome flats, nitrogen will still spill out. This is normal, but try to avoid it when the dewar is full. You can avoid some spilling by removing the telescope cover before filling the dewar, if conditions permit. 4. To avoid condensation or frost on the dewar window, be sure the defogging fan is running. 3.3. Potential Problems and the Dewar Vacuum As of January 2007 the GenI and GenII CCD dewars have new vacuum valves which share a single new gauge which can be connected to either dewar. The vacuum is good for several days without pumping as long as the dewar is not allowed to warm up. The LN2 hold time is about 24 hours. As a routine, keep filling the dewar every 24 hours or so as long as the camera is in use on the telescope. Leave the camera control software up and running on crux to check the temperature, with temperature regulation set for −110◦ C. For the GenI dewar be sure the defogging fan on the telescope tailpiece is running to keep frost from forming on the dewar window. This requires the CCD switch on the rack panel in the control room to be ON, to supply power to the camera controller and the defogging fan. The equipment for reading the vacuum gauge can usually be found in the storeroom on the dome floor level, or in the spectrograph room. It consists of a power supply transformer wired up to a 9-pin D connector and a digital multimeter. The D connector should be plugged into the connector on the vacuum gauge (before plugging in the power supply). When the meter is switched on to the 2VDC scale the voltage should ideally read 1.000V, which translates to roughly 0.01µ (0.01mTorr). Every increase of 1V is a factor of 10 in pressure, so 2V would be ∼ 0.1µ, 3V is ∼ 1µ, and 4V is ∼ 10µ. According to the dewar manual, problems (such as outgassing and difficuly holding LN2) set in when the pressure reaches 5µ, so for our purposes the vacuum is lost if the reading is over 4V. In practice, the dewar will probably not hold LN2 unless the reading is 2.5V or less. 92 To pump the dewar, connect the stainless steel hose from the vacuum pump to the dewar flange with a Quick Flange (QF) connector, but leave the dewar valve closed. The seal is made by compression of an O-ring between mating flanges by finger closure of a wingnut on a metal clamp, and the connectors on the dewar and the pump hose should be kept sealed with cover flanges when they are not connected to each other. Plug in the vacuum pump to a 220 VAC outlet, using the extension cord if necessary. Press the PUMPING button to turn it on. The vacuum pump is a two-stage pump system which includes a controller. The roughing pump operates by itself first. The turbopump should spin up automatically when the roughing pump has lowered the pressure far enough for the turbopump to safely operate. Allow the turbopump to evacuate the hose for at least 30 minutes. After that time, if the turbopump is spinning (check the speed indicator if you can’t hear it), the pressure should be low enough to safely open the vacuum valve on the dewar. (If the turbopump is not spinning, do not open the dewar vacuum valve! If you cannot find a leak in the hose or fittings that you can repair, the pump may need maintenance.) If the dewar pressure reading is not less than 3V (∼ 1µ) after 3 hours, there is probably a leak of some kind which must be fixed before the camera can be used. When the pressure reading has dropped to 2.5V, close the dewar valve, turn off the vacuum pump, and fill the dewar. Ideally, the dewar will fill completely and the pressure reading will drop to 1.0V (∼ 0.01µ). If the dewar does not fill completely in less than 20 minutes, let it cool down for an hour or more, check to see that the pressure is still low and pump again if necessary, then try filling it again. As long as the dewar is kept filled and the pressure reading remains less than 2.5V the camera should work properly. When turning off the vacuum pump, wait until all rotor motion has stopped completely before unplugging the cord from the power outlet. 4. Operating the CCD Camera 4.1. Login 1. Log onto crux as user genicam with password juju&u$r. 2. Before proceeding, insert a blank tape into the DAT drive and enter the command mt -f /dev/rmt/0n status in any terminal window to verify that the tape drive is working. (Check the label on the tape drive for the device name currently in use.) You should get a message resembling: crux% mt -f /dev/rmt/0n status Sony 4mm DAT tape drive: sense key(0x6)= Unit Attention file no= 0 block no= 0 residual= 0 retries= 0 If you don’t get the above message try power cycling the tape drive. Saving your data to tape is one of the last and most important things you’ll do at the end of the night, so it’s best to make sure this will go smoothly at the outset. 93 3. The home directory in which you will be working on crux is /crux/genicam. In this directory is the file login.cl, a startup file used by the IRAF program, and the subdirectory juju, which is used to store setup files for the camera controller. In addition to the Sun internal 19GB disk, there is also an external 34GB disk attached to crux which appears as a directory called /data. All raw image files should be stored in the subdirectory /data/genicam. In this directory (i.e. after entering cd /data/genicam), create a unique subdirectory for your images. 4.2. Starting IRAF First start the DS9 image display program by entering ds9 & at the prompt in a terminal window. Then open an xgterm terminal by entering xgterm &. In the xgterm window, from directory /crux/genicam, enter cl to start IRAF. To see a help page for any IRAF task, enter help task at the cl> prompt. One way to run any IRAF task is to enter epar task, edit any parameters that you want to set or change, then type :go and hit RETURN. Tasks can also be run directly from the IRAF command line. 4.3. Starting the Voodoo Program 1. Start the modified version of the Voodoo camera control program by entering the command juju in a terminal window. The Voodoo Main window should appear on the screen (Fig. 2). 2. Some configuration parameters for Voodoo may be set using the popup windows available from the menu bar of the Main window. First select Setup from the menu bar to bring up the Setup window (Fig. 3). Load the file /crux/genicam/juju/juju.setup and click Apply to initialize the camera controller, then close the Setup window. 3. The Subarray popup window will not do anything until the necessary readout instructions have been added to the code that is downloaded to the processors in the GenI controller. The Voodoo Focus Sequence will not work either, since it depends on the same subarray readout instructions. 4. Select Parameters from the menu bar to bring up the Controller Parameters window. Select the Temperature tab and set the array temperature control to -110 C (Fig. 4). Click Apply Above and close the Controller Parameters window. 5. Select Debug from the menu bar, then open the Developer Parameters window by selecting Development. Select the Gain tab, set the Low video gain button, then click Apply Above (Fig. 5). Close the Developer Parameters window. 6. If you would like your image headers to contain FITS keywords other than those required for basic formatting, you can use the FITS window (Fig. 6). If TCSLink is checked, the FITS header parameters labeled Universal Time, Local Sidereal Time, Equinox, Airmass, Hour Angle, Right Ascension, and Declination are updated automatically over a serial link to the telescope control PC at the beginning of each exposure or whenever you click Update. The filter parameters labeled Filter 1, Filter 2, Filpos 1, and Filpos 2 will be updated also, regardless of the setting of the TCSLink checkbox. The FITS header parameters with white backgrounds may be edited manually. 94 Figure 2. The Voodoo Main window. 95 Figure 3. The Voodoo Setup window. 96 Figure 4. The Voodoo Controller Parameters window, Temperature tab. Figure 5. The Voodoo Developer Parameters window, Gain tab. 97 Figure 6. The Voodoo FITS window. 98 Figure 7. 4.4. The Voodoo Filter Control window. Filter Control System The filter wheels inside the telescope tailpiece above the CCD camera shutter can be operated from the filter control panel on the south face of the tailpiece when the switches are set to LOCAL or from the filter PC computer in the control room when the switches are set to REMOTE. Filter wheel A (the lower one, also known as filter wheel 1) has 4 openings spaced at 90◦ intervals and holds 6-in square filters. Filter wheel B (the upper one, also known as filter wheel 2) has 6 openings spaced at 60◦ intervals and holds 4-in square filters. To load a filter into a filter wheel, first open the filter wheel access door (the rectangular panel above the filter control panel held shut by clamps) so you can see the filter wheels inside the tailpiece. Switch the filter wheel to LOCAL and use the SLEW button on the filter control panel to rotate it. Open the lock at the edge of the filter opening you select, slide the filter into the slot, then close and gently screw down the lock with your fingers. The filter opening in the telescope light path is the one diametrically opposite the one at the access door. A Filter Control window (Fig. 7) has been added to Voodoo to provide an interface to the filter control system using a serial link between crux and the filter PC. 99 1. To control the filter wheels remotely, begin by turning on the filter PC (white tower) underneath the table in the control room. The filter PC boots to a DOS prompt. 2. Enter cd c700\lotion at the DOS prompt to get to the correct directory. Then enter potion to start the version of the filter control program that operates with Voodoo. 3. The filter PC first checks for initialization: Assuming filter wheel positions 1,1 to start. If not, set positions on LOCAL ("GO HOME" buttons). Enter "Y" when ready to start. If necessary, go upstairs to the dome and HOME both filter wheels under LOCAL control. This sets filter positions 1,1 (filter openings numbered “1” in the telescope light path). Then switch both wheels back to REMOTE and go back down to the control room. 4. Now click Init in the Voodoo Filter Control window. This must be done to initialize the filter wheel positions to 1,1 in the Voodoo software. 5. To move the filter wheels, select the desired Filter Wheel position numbers with the radio buttons, then click Move. Voodoo calculates the necessary moves, sends commands to the filter PC, and updates the Filter Control display. Although the updates appear immediately in Voodoo, the filter PC monitor displays the actual move command while it is being executed and gives a confirmation when it is done. 6. The numerical filter positions and the corresponding descriptive labels in the text fields in the Filter Control window are always updated automatically in the Filter Control window and included as FITS header parameters FILPOS1, FILPOS2, FILTER1, and FILTER2. The descriptive labels may be edited to match the filters loaded in the wheels, and these configurations may be saved and loaded as filter setup files with extension *.flt using the Load and Save buttons. 7. The Home button moves the filter wheels to the initialized position 1,1. 8. The Exit button causes the filter PC program to quit. 4.5. Scope Control System A Scope Control window (Fig. 8) has been added to Voodoo to allow the user to load an object list and command the telescope to slew to a selected list object using the serial link to the telescope control PC. An object list must be a simple text file with extension *.lst, with one line per object. The format of each object line is arbitrary and may include any number of fields of any reasonable length, except that each line must include the RA and DEC separated by whitespace (spaces or tabs) only, each in sexagesimal format with no whitespace padding. 100 Figure 8. The Voodoo Scope Control window. 101 1. In the Voodoo Scope Control window, click Load to select and load an object list file. 2. Enter the Equinox of the coordinate list in the Equinox text field. This must be done only once per loaded list and may be changed at any time. 3. To slew the telescope to a list object, swipe the coordinate section of the object line with the mouse (RA and DEC fields together) so that it is highlighted, then click Slew. The slew commmand will be echoed in the main Voodoo Information Window and the TCS will immediately slew the telescope. As always, a slew can be aborted with the Stop slew command (8) from the TCS Movement menu. 4. Object lists cannot be edited or saved from the Scope Control window. 4.6. Taking an Exposure 1. Check Save to Disk in the Main window and enter the full pathname of your image directory and a beginning filename for your images. If Auto Incr is checked, the numeric part of the filename will be automatically incremented with each new exposure. Otherwise you must enter a new filename for each new image. 2. For normal exposures, check Open Shutter, enter the desired exposure time, and click Expose in the Main window. 3. Display and analyze the images with IRAF and DS9. 4.7. Ending a CCD Session 1. To copy your image files to DAT tape, change to your image directory in any teminal window, then use the unix command tar cvf /dev/rmt/0n . to write all your image files to tape. (This takes about half an hour for 100 images.) 2. After your images have been written to tape, rewind the tape and take the tape drive off line by entering mt -f /dev/rmt/0 rewoffl, then remove your tape from the drive. 3. Exit Voodoo (remember to home the filter wheels and exit the filter control system from the Filter Control window first), log out of IRAF, quit DS9, exit xgterm, and log out of the CDE window system. 102 Chapter 11 The GenII CCD Camera (Spectroscopy) 103 104 The GenII CCD Camera System (Spectroscopy) (Rev. August 17, 2011) 1. System Description The GenII CCD system uses the Generation II controller developed by San Diego State University (Leach group) and now managed under the company name of Astronomical Research Cameras, Inc. (ARC). The detector is an SI424A scientific grade CCD imager manufactured by Scientific Imaging Technologies, Inc. (SITe). This camera system is intended primarily use with the Fan Mountain Observatory Bench Spectrograph (FMOBS), which is described in detail elsewhere. The SDSU controller is mounted directly on a CCD liquid nitrogen dewar with a serial fiber optic communications link leading from the controller housing to a PCI interface card in a Sun Ultra5 computer. For operation with the GenII controller, the toggle switch on the back panel of the computer should be set to “GEN II”. The power supply for the controller is a gray metal box with a switch which must be turned on for the controller to operate. Other hardware details of the system will depend on the spectrograph setup. The Sun Ultra5 control computer is named crux and uses the Sun Solaris2.8 operating system with the CDE window system. The user interface to the CCD controller is a program called Voodoo developed by SDSU and modified locally for use at Fan Mountain. Images are stored on disk in FITS (*.fits) format and can be transferred from disk to magnetic tape (4mm DAT DDS4). A typical full frame requires 8.6MB of storage. Images can be displayed and analyzed using IRAF tasks. This manual does not explain the details of using IRAF, but IRAF has an extensive built-in help facility, and full documentation is available on the web at the IRAF Project Home Page. 2. CCD Camera Specifications Table 1 summarizes the current configuration of the CCD camera, chip, and dewar. Fig. 1 is a plot of quantum efficiency vs. wavelength for the CCD in the GENII camera. 105 Spec Dewar Value IR Labs liquid nitrogen cooled, 1 ℓ capacity heating resistor hold time ∼ 36 hours Chip SITe 2048 × 2048 CCD Imager back-illuminated, thinned to enhance blue response Operating Temp. unstable above −100◦ C optimal operating temperature ∼ −110◦ C lowest achievable temperature ∼ −134◦ C Format 2048 (cols) × 2049 (rows) 24 µm square pixels CTE 0.99998–0.99999 Dark Current negligible at −110◦ C Full well > 150, 000 electrons/pixel Readout maximum ADU = 65535 4 available readout amplifiers (A,B,C,D) single, dual, or quad readout configurable subarray readout capability Low Gain (C1S) Amp C, Gain Set 1.0, Slow Integrate, No MPP Bias 3989 ADU, Gain 6.1 e− ADU −1 , Read Noise 4.5 e− High Gain (C2S) Amp C, Gain Set 2.0, Slow Integrate, No MPP Bias 1237 ADU, Gain 2.8 e− ADU −1 , Read Noise 7.8 e− Table 1. Current configuration of the CCD chip and camera. 106 Figure 1. Plot of CCD chip quantum efficiency vs. wavelength. The relevant curve for our chip is the top solid curve. 3. The Dewar 3.1. Description The CCD is mounted on a cold finger in an evacuated chamber behind a fused silica window in a liquid nitrogen dewar and is cooled by direct contact of the cold finger with liquid nitrogen. The dewar, manufactured for ARC by Infrared Laboratories, Inc., has a capacity of 1 ℓ and a hold time of about 36 hours. The dewar is capable of cooling the CCD to a temperature as low as about −134◦ C, but normally a heating resistor in the dewar is used to regulate the CCD temperature to some optimal working value between −110◦ and −100◦ C. 3.2. Normal Operation 1. At least 24 hours before your scheduled observing night, send email to Nick Nichols ([email protected]) and ask him to make sure the CCD dewar is filled. Top off the dewar at the beginning of the night, and again at the end of the night as a courtesy to the next observer if observations are scheduled for the following night. 2. Filling the dewar takes about 15 minutes if it is still cold from the previous filling, but up to 40 minutes if starting from room temperature. It takes about 4 hours for the dewar to cool from room temperature to the optimal operating temperature of −110◦ C, so it is important to allow sufficient time for the cooldown before observing. 107 3. To fill the dewar, attach the connector at the end of the hose from the dewar to a 25ℓ LN2 tank and fill the dewar with liquid nitrogen until you see liquid spilling out the side vent of the dewar connector. It takes some time for the hose to cool sufficiently to allow nitrogen to pass without evaporating, and the connectors will become coated with frost. 3.3. Potential Problems and the Dewar Vacuum As of January 2007 the GenI and GenII CCD dewars have new vacuum valves which share a single new gauge which can be connected to either dewar. The vacuum is good for several days without pumping as long as the dewar is not allowed to warm up. The LN2 hold time is about 24 hours. As a routine, keep filling the dewar every 24 hours or so as long as the camera is in use on the telescope. Leave the camera control software up and running on crux to check the temperature, with temperature regulation set for −110◦ C. (For the GenI dewar be sure the defogging fan on the telescope tailpiece is running to keep frost from forming on the dewar window. This requires the CCD switch on the rack panel in the control room to be ON, to supply power to the camera controller and the defogging fan.) The equipment for reading the vacuum gauge can usually be found in the storeroom on the dome floor level, or in the spectrograph room. It consists of a power supply transformer wired up to a 9-pin D connector and a digital multimeter. The D connector should be plugged into the connector on the vacuum gauge (before plugging in the power supply). When the meter is switched on to the 2VDC scale the voltage should ideally read 1.000V, which translates to roughly 0.01µ (0.01mTorr). Every increase of 1V is a factor of 10 in pressure, so 2V would be ∼ 0.1µ, 3V is ∼ 1µ, and 4V is ∼ 10µ. According to the dewar manual, problems (such as outgassing and difficuly holding LN2) set in when the pressure reaches 5µ, so for our purposes the vacuum is lost if the reading is over 4V. In practice, the dewar will probably not hold LN2 unless the reading is 2.5V or less. To pump the dewar, connect the stainless steel hose from the vacuum pump to the dewar flange with a Quick Flange (QF) connector, but leave the dewar valve closed. The seal is made by compression of an O-ring between mating flanges by finger closure of a wingnut on a metal clamp, and the connectors on the dewar and the pump hose should be kept sealed with cover flanges when they are not connected to each other. Plug in the vacuum pump to a 220 VAC outlet, using the extension cord if necessary. Press the PUMPING button to turn it on. The vacuum pump is a two-stage pump system which includes a controller. The roughing pump operates by itself first. The turbopump should spin up automatically when the roughing pump has lowered the pressure far enough for the turbopump to safely operate. Allow the turbopump to evacuate the hose for at least 30 minutes. After that time, if the turbopump is spinning (check the speed indicator if you can’t hear it), the pressure should be low enough to safely open the vacuum valve on the dewar. (If the turbopump is not spinning, do not open the dewar vacuum valve! If you cannot find a leak in the hose or fittings that you can repair, the pump may need maintenance.) If the 108 dewar pressure reading is not less than 3V (∼ 1µ) after 3 hours, there is probably a leak of some kind which must be fixed before the camera can be used. When the pressure reading has dropped to 2.5V, close the dewar valve, turn off the vacuum pump, and fill the dewar. Ideally, the dewar will fill completely and the pressure reading will drop to 1.0V (∼ 0.01µ). If the dewar does not fill completely in less than 20 minutes, let it cool down for an hour or more, check to see that the pressure is still low and pump again if necessary, then try filling it again. As long as the dewar is kept filled and the pressure reading remains less than 2.5V the camera should work properly. When turning off the vacuum pump, wait until all rotor motion has stopped completely before unplugging the cord from the power outlet. 4. Operating the CCD Camera 4.1. Login 1. Log onto crux as user bench with password me4bench. 2. Before proceeding, insert a blank tape into the DAT drive and enter the command mt -f /dev/rmt/0n status in any terminal window to verify that the tape drive is working. (Check the label on the tape drive for the device name currently in use.) You should get a message resembling: crux% mt -f /dev/rmt/0n status Sony 4mm DAT tape drive: sense key(0x6)= Unit Attention file no= 0 block no= 0 residual= 0 retries= 0 If you don’t get the above message try power cycling the tape drive. Saving your data to tape is one of the last and most important things you’ll do at the end of the night, so it’s best to make sure this will go smoothly at the outset. 3. The home directory in which you will be working on crux is /crux/bench. In this directory are the directories fobos, which may be used to store setup files for the camera controller, and iraf, which contains the file login.cl, a startup file used by the IRAF program. In addition to the Sun internal 19GB disk, there is also an external 34GB disk attached to crux which appears as a directory called /data. All raw image files should be stored in the subdirectory /data/bench. In this directory (i.e. after entering cd /data/bench), create a unique subdirectory for your images. 109 4.2. Starting IRAF First start the DS9 image display program by entering ds9 & at the prompt in a terminal window. Then open an xgterm terminal by entering xgterm &. In the xgterm window, from directory /crux/bench/iraf, enter cl to start IRAF. To see a help page for any IRAF task, enter help task at the cl> prompt. One way to run any IRAF task is to enter epar task, edit any parameters that you want to set or change, then type :go and hit RETURN. Tasks can also be run directly from the IRAF command line. 4.3. Starting the Voodoo Program 1. Start the Voodoo camera control progam by selecting the Voodoo icon from the Gnome control panel. The Voodoo Main window (Fig. 2) should appear on the screen. 2. Many configuration parameters for Voodoo may be set using the popup windows available from the menu bar of the Main window. First select Setup from the menu bar to bring up the Setup window (Fig. 3). Load the file /crux/bench/fobos/C1S.setup for Low Gain or the file /crux/bench/fobos/C2S.setup for High Gain, and click Apply to initialize the camera controller, then close the Setup window. 3. Select Parameters from the menu bar to bring up the Controller Parameters window. Select the Temperature tab, set the array temperature control to -110.0 C, and click Apply Above (Fig. 4). Select the Readout tab, choose Amplifier C, for example, and click Apply Above (Fig. 5). This currently seems to be the best readout amplifier for general purposes. Close the Controller Parameters window. 4. Select Debug from the menu bar, then open the Developer Parameters window by selecting Development. Select the Gain tab and set, for example, Video Gain 1.0 and Integrator Speed Slow, then click Apply Above (Fig. 6). Close the Developer Parameters window. 5. Select Subarray from the menu bar to bring up the Subarray window and configure the subarray as desired. See Fig. 7 for an example. Click Apply to apply the settings. To revert to Full Array operation, select Full Array and click Apply. Close the Subarray window. 6. If you would like your image headers to contain FITS keywords other than those required for basic formatting, you can use the FITS window (Fig. 8). If TCSLink is checked, the FITS header parameters labeled Universal Time, Local Sidereal Time, Equinox, Airmass, Hour Angle, Right Ascension, and Declination are updated automatically over a serial link to the telescope control PC at the beginning of each exposure or whenever you click Update. The FITS header parameters with white backgrounds may also be edited manually. 110 Figure 2. The Voodoo Main window. 111 Figure 3. The Voodoo Setup window. 112 Figure 4. The Voodoo Controller Parameters window, Temperature tab. Figure 5. The Voodoo Parameters window, Readout tab. 113 Figure 6. The Voodoo Developer Parameters window, Gain tab. Figure 7. The Voodoo Subarray window. 114 Figure 8. The Voodoo FITS window. 115 Figure 9. 4.4. The Voodoo Scope Control window. Scope Control System A Scope Control window (Fig. 9) has been added to Voodoo to allow the user to load an object list and command the telescope to slew to a selected list object using the serial link to the telescope control PC. An object list must be a simple text file with extension *.lst, with one line per object. The format of each object line is arbitrary and may include any number of fields of any reasonable length, except that each line must include the RA and DEC separated by whitespace (spaces or tabs) only, each in sexagesimal format with no whitespace padding. 1. In the Voodoo Scope Control window, click Load to select and load an object list file. 2. Enter the Equinox of the coordinate list in the Equinox text field. This must be done only once per loaded list and may be changed at any time. 3. To slew the telescope to a list object, swipe the coordinate section of the object line with the mouse (RA and DEC fields together) so that it is highlighted, then click Slew. The slew commmand will be echoed in the main Voodoo Information Window and the 116 TCS will immediately slew the telescope. As always, a slew can be aborted with the Stop slew command (8) from the TCS Movement menu. 4. Object lists cannot be edited or saved from the Scope Control window. 4.5. Taking an Exposure 1. Check Save to Disk in the Main window and enter the full pathname of your image directory and a beginning filename for your images. If Auto Incr is checked, the numeric part of the filename will be automatically incremented with each new exposure. Otherwise you must enter a new filename for each new image. 2. For normal exposures, check Open Shutter, enter the desired exposure time, and click Expose in the Main window. 3. Display and analyze the images with IRAF and DS9. 4.6. Ending a CCD Session 1. To copy your image files to DAT tape, change to your image directory in any teminal window, then use the unix command tar cvf /dev/rmt/0n . to write all your image files to tape. (This takes about half an hour for 100 images.) 2. After your images have been written to tape, rewind the tape and take the tape drive off line by entering mt -f /dev/rmt/0 rewoffl, then remove your tape from the drive. Exit Voodoo, log out of IRAF, quit DS9, exit xgterm, and log out of the CDE window system. 117 118 Chapter 12 The Fan Observatory Bench Optical Spectrograph (FOBOS) 119 120 Fan Observatory Bench Optical Spectrograph (FOBOS) (Rev. August 06, 2007) The Fan Observatory Bench Optical Spectrograph (FOBOS) is a fiber–fed, bench–mounted, single–object spectrograph. The instrument is designed to observe point sources at moderate resolution to V ∼ 14, although extended objects can also be observed if knowledge of the precise spatial sampling is not important. This manual is intended for the observer and gives the information required to operate the instrument night to night. Although the intention is to instruct a true beginner, reading the manual is absolutely no substitute for hands-on training. NO PERSON should attempt to use the instrument for the first time without having an experienced observer present for supervision. Ideally, anyone interested in using the instrument should accompany an experienced observer for at least one night prior to observing on their own. Additional detailed technical information can be found in the “FOBOS Technical Reference”, in Jeff Crane’s dissertation, and in the FOBOS primary reference publication (PASP, 2005, 117, 526). Please e-mail Jeff with any suggestions concerning this manual or the instrument itself. Contact Jeff Crane Steve Majewski David McDavid Ricky Patterson Phone E-mail Role ... [email protected] Instrument Designer 924-4893 [email protected] Principal Investigator 924-4899 [email protected] 40” & Instrument Support 924-4914 [email protected] Co-Investigator 121 1. Instrument Overview FOBOS is operated from the 40” Control Room on the third floor of the observatory. Parts of the instrument itself are located on all four floors of the building. FOBOS can be broken up into three main components: the Focal Plane Module, the Fiber Train, and the Bench Spectrograph itself (See Figure 1). FMO 40" Telescope Tailpiece and Focal Plane Module Fiber Train Spectrograph Enclosure Bench Spectrograph Telescope Pier Figure 1. The complete FOBOS system is shown on the 1-meter telescope. The building and telescope pier are shown in cross-section. The fiber train runs from the Focal Plane Module through the telescope’s polar axis (not shown) and down the side of the telescope pier to the Bench Spectrograph enclosure. 1.1. The Focal Plane Module The Focal Plane Module (Figure 2) mounts to the base of the telescope tailpiece at the Cassegrain focus. Its functions include: • Providing a mechanism for target/fiber alignment • Providing calibration light for the spectrograph A movable fold mirror carriage just above the telescope’s focal plane enables three separate optical paths: 122 Figure 2. Diagram of the Focal Plane Module, viewed from the West side. • Primary (coarse) Acquisition: The telescope image plane is demagnified 5× and viewed by an SBIG STV video camera, yielding a 6.0×4.4 arcmin field of view. The target star can be viewed, identified, and roughly positioned on the fiber of choice. The approximate poisition of the preferred fiber (Fiber 1, positioned along the telescope’s optical axis) is marked on the video monitor in the control room. • Secondary (fine) Acquisition: Telescope light comes into focus in the plane of the fiber ferrules. The guide fibers (see section 1.2.) are monitored with a second SBIG STV camera while the alignment of the target star is fine-tuned. When alignment is achieved, the telescope autoguider may be engaged if necessary, and observing can begin. • Calibration: Three arc lamps and a quartz-tungsten-halogen (QTH) lamp are available for calibrations. These lamps illuminate an opal diffusing glass, which in turn is imaged onto the plane of the Focal Plane Ferrules. Calibration light is then transmitted to the Bench Spectrograph. 123 Science Fiber Guide Fibers Teflon Tubing Attachment Stainless Steel Capillary Tube Figure 3. The focal plane fiber ferrule is shown in isometric projection in full and in cross-section. The teflon tube–encased fibers enter at the base where the teflon tubes are epoxied to the aluminum. The fibers themselves are then brought to a close–packed hexagonal array in the capillary tube extension. 1.2. The Fiber Train The main length of the fiber train consists of 7 (redundant) “science fibers” that transmit light from the telescope to the Bench Spectrograph. In the telescope’s focal plane, each science fiber is mounted in a ferrule (Figure 3) and surrounded closely by 6 short guide fibers, which can be used for fine-tuning the target alignment. Although there are several fibers that run from the telescope’s focal plane to the bench spectrograph, only one fiber may be used at a time to collect light from a target. The fibers are fixed and cannot be independently positioned. At present, only five of the seven science fibers are functional, and only two are optimized for observation of science targets; the remaining three are intended for collection of diffuse background (sky) emission for subtraction during data processing. At the telescope level, power and communication cables are tethered to the fiber train as it drapes from the Focal Plane Module to the fork of the telescope (Figure 4). When the Focal Plane Module is attached to the telescope’s tailpiece, the fiber train should always be attached to the left arm of the telescope fork using the eyebolts in the fork and snap hooks attached to the fiber train. When the Focal Plane Module is not in use, it should be parked on its lift system to the left of the fork and the fiber train should be detached from the four eyebolts. It is VERY important to make sure that while slewing the telescope, the fiber train does not catch on any foreign objects, including the tailpiece or hardware attached to the telescope. Constructing the fiber train took several hundred hours of work, and great care should be taken to make sure it does not become damaged. 1.3. The Bench Spectrograph The Bench Spectrograph (Figure 5) sits on a vibrationally isolated optical table in a stable, environmentally controlled enclosure. The Fiber Train attaches to the Science Fiber Mount (Figure 6), where the science fibers are arranged in a linear, vertical array. By default, the fiber ends themselves define the 124 Telescope Fork Fiber Train Focal Plane Module Control Box Focal Plane Module STV control boxes Figure 4. The Focal Plane Module is shown attached to the 40” tailpiece. The Fiber Train drapes freely to the left side of the telescope’s fork, where it attaches to eye bolts using snap hooks. When the spectrograph is unmounted, the Fiber Train should be detached from the fork. “entrance slit”. However, immediately in front of the ferrules is positioned a slot for an optional entrance slit mask. Following the slit position, there are two slots for optional interference filters and an opal glass used for making “milky flats”. The instrument’s shutter is attached to the front of the Science Fiber Mount. The Collimator Mount holds a 100mm diameter, 350mm focal length achromatic doublet lens and an iris diaphragm. The focus of the collimator and iris diameter should not normally need to be adjusted by the observer during an observing run. The Grating Mount contains a rotation stage that can hold one reflection grating from the inventory at a time. The primary setup 1 calls for a 100×100mm grating with 1200 lines/mm blazed for 6000˚ A. The Dewar Mount rides on a linear rail that pivots directly under the diffraction grating’s reflective surface. A 135mm f/2 SLR lens on the front of the Dewar Mount focuses diffracted light onto the CCD. The SLR lens front focus should always be set to ∞. The rear focus, once set by technical staff, should not be adjusted. The azimuthal rotation of the CCD with respect to the optical axis of the SLR lens may be adjusted using the micrometer on the 1 Throughout this manual, reference will be made to the “primary” setup, which is the instrument configuration designed for use by the Grid Giant Star Survey (GGSS): 4700–6700˚ A coverage at R ∼ 1200. 125 CCD dewar Dewar Mount Grating Mount Science FIber Mount Grating cover Fiber Train SLR lens CCD power supply SLR cover Celestron telescope Collimator Mount Figure 5. The Bench Spectrograph is shown from overhead. The fiber train attaches to the Science Fiber Mount assembly on the right. The CCD and camera rotate on a pivot arm (not visible in this view) to allow a range of collimatorgrating-camera angles. The Celestron telescope is used by technical staff to focus the collimator. top of the mount. This may be necessary to align the spectra along rows of the CCD. The azimuthal rotation of the CCD with respect to the optical table may be adjusted using a micrometer on the rear of the Dewar Mount. This may be necessary to account for tilt in the focal plane, but should not be adjusted after the start of a run. The detector is a 2048×2048 SITe CCD with 24 µm square pixels operated by an SDSU CCD Laboratory (Bob Leach) Generation II controller. Note that because of non-symmetric vignetting on the red side of the chip, the full 2048 columns are not actually illuminated. The actual usable portion of the spectra will cover something like 1850-1900 pixels, and the quoted wavelength coverage will drop by an equivalent amount. 2. Available Configurations FOBOS was designed to collect moderate resolution spectra of candidate K giants for the Grid Giant Star Survey. Spectra collected for this project in the Southern hemisphere cover the region ∼4700–6700 ˚ A with ∼1 ˚ A/pixel dispersion. To match these spectra, one diffraction grating was chosen for work in first order with no interference filter necessary. As the instrument’s usability is demonstrated, additional diffraction gratings, interference filters, and optional slit masks may be added to the inventory to allow a variety of different 126 Filter Slot #2 Shutter Figure 6. Slit mask or dummy Filter Slot #1 Slit positioner cover Filter/Slit removal tool Fiber Train Science fiber array handle Science Fiber Mount shown from above with top cover removed. configurations capable of covering the full optical wavelength range. As the inventory changes, this section will be expanded to more fully describe the various configurations available to observers. Grating Lines/mm Blaze δ 1200@157 1200 15.7◦ 1200@211 1200 21.1◦ 1200@267 1200 26.7◦ Table 1. Blaze λ 4500 ˚ A 6000 ˚ A 7500 ˚ A Ruled area 100×100 mm 100×100 mm 154×128 mm FOBOS diffraction grating inventory. Filter Shape Width Thickness GG-420 square 25.4 mm 3 mm RG-610 round 25.4 mm 3 mm Opal square 25.4 mm 3 mm Table 2. 3. FOBOS filter inventory. Setting Up Please take care to keep the spectrograph room clean. Do not eat, drink, or smoke in the room. Every time you enter, clean the soles of your shoes by planting your feet firmly on the sticky mat in the entryway. If the mat does not feel sticky, step on a different area. When no sticky surfaces remain, peel off and dispose the top layer of the mat. 127 Figure 7. Total transmission through the interference filters. Slit Width None 200 µm 1 100 µm Table 3. 3.1. Throughput 100% 60.8% FOBOS slit mask inventory. Filling the Dewar Standard safe handling procedures should be followed when working with liquid Nitrogen. In the spectrograph room, roll the 25-liter dewar to the end of the optical table nearest the storage area. Insert the “stinger” into the CCD dewar’s fill tube. Tighten the threaded connector with the spill vent pointing toward the wall and away from the spectrograph optics. Fill the CCD dewar until ℓN2 begins to spill out of the connector’s side vent. This will probably take about 10 minutes if the dewar is already cool. Allow the hose to thaw until flexible before removing the stinger — otherwise you’re likely to break the fill hose in two! 3.2. Enabling the Vibration Isolator The Bench Spectrograph’s optical table is mounted on a pneumatic vibration isolator. This provides some dampening of vibrations in the floor that would otherwise translate to vibrations in the optics on the table. To enable the system, first make sure that the isolator’s air tube is attached to the air compressor’s air hose dangling from the ceiling of the spectrograph room. Insert the plastic 128 air tube firmly into the brass and red plastic fitting on the end of the thick black air compressor hose. On the ground floor of the observatory next to the the telescope’s support column, find the air compressor. Make sure that the water drain valve on the bottom of the air tank is closed. Also make sure the regulator is closed (turned fully clockwise). Turn the OFF/AUTO lever to AUTO and let the tank’s pressure build. The internal pressure should build to about 125 psi before the compressor will turn off. Now open the regulator to pressurize the hose leading to the spectrograph room to about 60 psi. Return to the spectrograph room and make sure that the optical table has been elevated about 3/8”. If the lift distance varies greatly from 3/8” the pressurizing or adjustment screws on the leveling arms of the isolator may need to be adjusted. Listen for air leaks in the supply line connection. If you hear one, you may need to tighten the connection. 3.3. Preparing the Spectrograph Room Turn off the air conditioner and close and clamp the A/C door (Figure 8). Turn off the air cleaner and the dehumidifier. Turn on the power switch to the CCD (gray box next to the dewar on the optical table) if it is not already on. Grab a flashlight. Turn off the lights. Carefully remove the cover of the SLR lens on the front of the CCD dewar. Be careful not to rotate the SLR lens itself; the front focus of the SLR lens should always be set to ∞. Very carefully remove the grating cover and set it aside. Be very, very careful not to touch the diffraction grating. The grating cost several thousand dollars and cannot be cleaned! If you touch it, it will have your greasy fingerprints on it for the remainder of its lifetime. When you exit the room, turn off the light and pull both doors firmly closed behind you. 3.4. Computer Start-up Follow the standard start-up procedure for powering on the telescope and tailpiece. Turn on the Dell autoguider PC, making sure that the keyboard/monitor switch is turned to the correct position. Once the computer comes up, flip the monitor/keyboard switch and turn on the TCS computer. Start TCS. Turn on the CCTV monitors for the autoguider STV, dome camera, and FOBOS STVs. Turn on the FOBOS PC. Power on the Sun workstation named crux. Log in as user bench. Contact one of the people listed on the front of this manual or a previous FOBOS observer to get the account password. Start the Voodoo CCD control software (see documentation for the GenII CCD camera), DS9, and IRAF in an xgterm. If it’s not already on, turn on the FMO EMCS (Environment Monitoring and Control System) PC and start the EMS software. After the dome room has been prepared (Section 3.5.), establish a connection with the autoguider STV on the Autoguider PC, and with the two FOBOS STVs on the FOBOS PC. The FOBOS coarse acquisition STV communicates with the PC through the COM1 port while the Guide Fiber STV communicates through the COM2 port. 129 Air conditioner A/C door Air cleaner Dehumidifier Figure 8. The back right corner of the spectrograph room. Environmental control devices should be turned off at dusk prior to observing, and the air conditioner frame door should be closed and latched. During the day when observing is not taking place, all environmental control devices should be turned on again. 3.5. Preparing the Dome Room Around sunset, prop the doors to the catwalk open. Open the dome slit and detach the power cord from the dome. Turn on the telescope tube fans if they are not already on. Check the fiber train to make sure that it is hanging properly. It should be attached to the left arm of the fork in several places, almost all the way to the telescope’s declination axis. Slew the telescope to the north and remove the cover. Remove the cover of the 8” autoguider telescope and send the telescope to zenith again. Turn on the power to the telescope autoguider STV control box on. Make sure that the power to the spectrograph’s two STV cameras and the electronics control box is on. The power strip attached to the right (West) side of the primary mirror cell should be on as should the power switches on the STV control boxes. Note that the “CCD” power switch at the bottom of the electronics rack in the control room must be turned on before power can be supplied to the Focal Plane Module and STV cameras. Make sure the spectrograph’s electronics control is set to “remote”. Open the in-tailpiece shutter using the switch near the back left side of the primary mirror cell. Turn off the air conditioner power on the left wall of the dome room. Set the humidistat-controlled heat lamps to the off position. Turn off the lights and shut the door to the dome room on your way out. 130 Tailpiece Filter Control Autoguider STV Monitor TCS Monitor FOBOS STV switch FOBOS STV Monitor FMOEMCS Monitor FMOEMCS PC crux peripherals FOBOS PC crux power TCS PC crux CPU Telescope Motor Control crux Monitor Instrument Power Intercom Autoguider/TCS switch Autoguider/TCS Monitor FOBOS Paddle FOBOS Monitor Telescope Paddle Figure 9. The 40” control center. All but the filter wheel control PC are used during operation of the spectrograph. 3.6. Please please please... Don’t touch the surface of diffraction grating, SLR lens glass, or collimator glass. Don’t crush, yank, or tightly bend the PVC pipe containing the fiber optics. The fleas of a thousand rabid camels will be set upon your carcass if you break the fiber optics. 4. Observing 4.1. What Data Should You Collect? For any scientific target, it’s a good idea to split up your observations into three separate exposures to be combined later. This simplifies cosmic ray removal. To adequately calibrate your spectra, you will want to take the following additional data: • Bias frames. Take at least one set of bias frames (zero second exposures) each night. A good rule of thumb is to take 10 frames and then median combine them later. • Milky flats. During the evening before observing, insert the opal glass in Slot 2 in the Science Fiber Mount on the optical bench. Be sure to replace the cover on the mount. 131 Move the fold mirror array in the Focal Plane Module to the Calib position and turn on the quartz (QTH) lamp. Take a few exposures of a few thousand counts each. In the primary setup, exposure lengths of about 5 minutes should suffice. These can be median combined later to produce a flat field image. You can also use the daytime sky to produce milky flats. Although the required integration times will be longer for the daytime sky, the resulting flats may be more evenly illuminated. Remember to remove the opal glass and replace the mount cover when you are finished! • Quartz lamp exposures. The quartz lamp spectra are bright continua that can be used to estimate fiber-to-fiber relative throughput differences and to determine reference traces for extracting faint object and arc lamp spectra. With the Focal Plane Module’s fold mirror carriage in the Calib position, turn on the quartz (QTH) lamp. 1 second exposures should suffice. Ideally, the spectrograph should be stable enough that only a single QTH lamp exposure per night is required. However, until the instrument stability has been verified, it’s a good idea to take several throughout the night. Note that for the determination of relative fiber throughput, daytime sky (solar) spectra will be more accurate. • Solar spectra. In addition to being useful wavelength calibration spectra, observations of the daytime sky will provide more accurate determinations of the relative throughputs of the various fibers during data reduction. The calibration lamp system does not illuminate each science fiber completely evenly. If the relative fiber throughput is important to you (as it should be if you want accurate sky subtraction), observations of the daytime sky (solar spectrum) will be useful. These would then replace the Quartz lamp exposures. • Camparison (arc lamp) exposures. Three independent comparison sources are available: Neon (Ne), Argon (Ar), and Xenon (Xe). Depending on your instrument setup, some lamp(s) may be more useful than others. In the primary setup, it appears that a 60-second exposure suffices, with the Ne lamp turned on for a fraction of a second (it is much brighter than the others). To accomplish this, turn on all three lamps, set the CCD exposure time at 60 seconds, and start the exposure. When you hear the shutter open through the intercom, immediately turn off the Ne lamp. Again, given good instrument stability, only one comparison lamp exposure per night should be necessary, but it is advised that multiple exposures be taken throughout the night until confidence in the stability has been established. • Radial velocity standards. If you’re doing radial velocity work, you will want to observe some number of radial velocity standards for comparison later. A good list is provided in the Astronomical Almanac. • Flux standards. If you are doing work where the absolute flux of the star, or the relative flux between lines are required, you will want to observe flux standards so that the instrumental, wavelength-dependent efficiency profile can be removed. Multiple literature references are available for selecting flux standards, one of which is: Massey, Strobel, Barnes, and Anderson, 1988, ApJ, 328, 315. 132 4.2. Spectrograph Control System During normal observing, the user will need to control the Focal Plane Module fold mirror carriage, wavelength calibration lamps, quartz lamp, coarse and fine acquisition cameras, autoguider camera and telescope, 40” telescope, and SITe CCD. The fold mirror carriage and calibration lamps may be controlled either by using the electronics control panel attached to the Focal Plane Module or by using the remote paddle in the control room (Figure 9). A Local/Remote switch on the control panel determines which location has control. In both places may be found ON/OFF switches for each of the four calibration lamps (QTH, Ne, Ar, Xe) and three push buttons that send the mirror carriage to its three available positions. The three carriage positions are labeled Calib, Observe, and Acquire. In the Calib position, a fold mirror enables the calibration lamp system. In the Observe position, the focal plane ferrules are exposed to light from the telescope. If a target is aligned on the end of a ferrule, light will find its way to the Guide Fiber STV camera and Bench Spectrograph. In the Acquire position, a fold mirror enables the primary acquisition (coarse) system and the Acquisition STV will show a 6’×4.4’ telescope field of view. When the carriage is at any one position, the red LED above that button will glow. If the FP Module is powered on but none of these LEDs is lit, the carriage may be stuck between its three normal stops. In this case, a manual switch on the control panel can be used to drive the carriage until one of the LEDs lights up. If the carriage is run past the extreme positions toward its hard limits, limit switches will disable the motor. In this case, a limit override switch on the control panel must be depressed and the carriage driven manually back away from the limit. Be very careful not to drive the carriage to its hard limits! If you do, you may destroy the motor or drive nut. The FOBOS STVs may be controlled by either the control boxes attached to the Focal Plane Module or by the STV Remote software on the FOBOS PC. Similarly, the autoguider STV may be operated by the control box attached to the telescope tailpiece or by the STV Remote software installed on the Autoguider PC. Other autoguider controls include a fine focus adjustment and East/West slew controlled by hand paddles in the control room. See the autoguider documentation for instructions about running that system. The 40” telescope is controlled by the DFM Telescope Control System (TCS) and by hand paddles in the dome and control rooms. The SITe GenII CCD is controlled by the Sun workstation crux. See the manuals pertaining to those systems for more information. 4.3. Software Initialization In an xgterm on the crux workstation, change to the $HOME/iraf/ directory and start IRAF with the cl command. Within IRAF, change to the /data/bench/ directory and create a new directory named for today’s date. Start the ds9 software for image display. Note that because crux is set up for 24-bit color, ximtool and SAOimage will not work. 133 Refer to “The GenII CCD Camera System (Spectroscopy)” manual for detailed instructions about running the CCD control software, Voodoo. For spectrograph work, Amplifier C is preferred with Gain 1.0 and Slow Integration speed (setup file /crux/bench/fobos/C1S.setup). For faint targets, Gain 2.0 may be useful (setup file /crux/bench/fobos/C2S.setup). Set the CCD for subarray readout with dimensions 2048×200 centered at [1024, 1024]. Set the Bias Position at 2080 and the Bias Width at 20. In the FITS setup menu, load the file /crux/bench/fobos/FOBOS-fits.par and check the TCS Link box. These steps will ensure that your image headers have the keywords required for spectral reductions. Make sure the Open Shutter, Beep, and Save to Disk boxes are checked in the main Voodoo window. Set the output directory to /data/bench/date today/ and initialize the file name to something like ccd1001.fits. Note that IRAF wants the image filename extensions to be “fits” and not “fit”. The STV cameras used in the spectrograph and with the autoguider may all be controlled using the STV Remote software. Run the software on the autoguider PC and connect to the guider STV through port COM1. On the FOBOS PC, run two instances of the software. Connect to the Acquisition STV through COM1 and the Guide Fiber STV through COM2. Refer to the 40” manual for further instructions about running the autoguider. For the spectrograph STVs, it is not important to set the correct Date/Time, telescope focal length, etc. You may begin imaging with the STV cameras immediately after establishing successful links. Click Image and then click Parameter repeatedly to see the adjustable parameters. Set each parameter by clicking the Value button. Choose the “Normal” zoom mode and the ×2 gain setting. Finally, click Image again to start the continuous video stream to the monitor. 4.4. Calibration Lamp Exposures You will want to take a set of calibration images during or before each night of observing. These should ideally be done after the spectrograph room has been prepared for observing and the air has settled (i.e. when the spectrograph room is in a state most similar to nighttime observing). A set of milky flats should probably be taken shortly after the room is prepared in the evening. An opal glass filer must be placed in Filter Slot 2 (Figure 6) and the top of the Science Fiber Mount replaced. Move the mirror carriage to the Calib position and turn on the QTH lamp. Take a series of exposures with a few thousand counts each. Remove the opal glass filter using the threaded brass tool next to the Science Fiber Mount and replace the top. Allow some time for the room to settle before taking additional calibration or targeted spectra. Ideally, the instrument should be so stable that a single QTH lamp spectrum and a single wavelength calibration lamp exposure taken at the beginning of the night would suffice to calibrate the entire night’s data. However, until instrument stability can be established, it is advised the QTH and arc lamp exposures be taken several times during the night. To do so, make sure the mirror carriage is in the Calib position. To take a QTH exposure, turn 134 Figure 10. Full view of a 1 second QTH lamp exposure in a 2048×200 pixel subarray centered at [1024, 1000]. on the QTH lamp and set the exposure time to something like 1 second. The wavelength calibration spectra are slightly trickier. In the primary instrument setup, the Neon lamp is considerably brighter than both the Argon and Xenon lamps. Set the exposure time to 60 seconds or more. Turn on all three arc lamps. Make sure the intercom to the spectrograph room is on and the volume is turned up. Start the exposure and listen for the shutter to open. As soon as the shutter opens, turn off the Neon lamp. Leave the other two on for the duration of the exposure. Figure 11. setup. 4.5. Extracted raw Neon/Argon/Xenon spectrum taken with the primary Telescope Coordinate Initialization Following the normal start-up procedure for the 40” telescope, align the telescope on a known, bright star using the finder scope. Move the fold mirror carriage to the Acquire 135 position and begin imaging with the Acquisition STV. Select input 1 for the FOBOS STV monitor. The bright star should be in view. Move the telescope using the hand paddle until the star is centered in the STV field of view. Now enter the star’s coordinates in the TCS’s telescope position initialization function. Important: For the first few times the telescope is slewed to a new position, every time a large (> 30◦ ) slew is performed, and especially when large slews toward or away from the Northwest are performed, walk up to the dome and make sure the fiber train does not get caught on the telescope, tailpiece, or any other foreign object. 4.6. Focal Plane Module Focus The Focal Plane Module must be focused. This can be accomplished by moving the telescope’s tailpiece focus until the bright star used for coordinate initialization is in focus. The distance from the fold mirror in the carriage to the focal plane ferrules is the same as the distance from the mirror to the object plane of the coarse acquisition system. Therefore, focusing the image on the STV camera has the effect of bringing the ferrules into the telescope’s focal plane. Note that there are aberrations in the image produced by the very simple optical system used for coarse acquisition. Stars will appear point-like in some areas of the image, but may have a ringlike appearance with a bright, off-center core in other areas. When focusing the instrument, attention should be paid only to the bright core of the star, or better — the star should be positioned in the less aberrated area of the camera toward the lower third of the monitor. On 13 Oct 2003, with an exterior temperature of ∼ 60◦ F, the spectrograph focus was at ∼ 3350. The star can be focused by eye, but perhaps a more accurate method is to use the “Optical Quality” mode built in to the STV controller. Move the telescope to position the star on the screen in an area where the optical aberrations appear minimal, but not too close to the edge. Press the Monitor button. Press the Parameter button until you see “OPTICAL QLTY”. Push the Value button. The STV should detect the star and begin monitoring its profile. Adjust the telescope’s focus while noting the change in the FWHM reported by the STV. Set the focus so that the FWHM is minimized. Note that the actual number reported is meaningless unless you enter the telescope parameters in the STV’s Setup menu (not required, but may be interesting). 4.7. Coarse Acquisition Once the telescope position has been initialized, coarse target acquisition may commence. Slew the telescope to the target’s coordinates. Make sure the STV monitor switch is set to input 1. The target should be in view. If it is relatively faint, you may need to bump up the STV exposure times to see it. Two science fibers are available for targeted acquisition. These are fibers 1 and 4 in Figure 12. For each of these ferrules, the science fiber is intact and the guide fibers are properly aligned around them. Fibers 2, 3, and 5 have functional science fibers, but the guide fiber arrangements are flawed, so the prescribed fine alignment procedure will not work. However, 136 South 2 1 6 East 3 4 7 West 5 North Figure 12. Top view of the Focal Plane Ferrule array. these can be used to collect sky spectra for background removal during processing. Fibers 6 and 7 are completely nonfunctional. The positions of Fibers 1 and 4 have been marked on the TV monitor with a grease pencil, with Fiber 1 being nearest the center. Using the hand paddle, move the telescope to position the target over the desired focal plane ferrule position. Fiber 1 appears to have the best throughput, so it is preferred. 4.8. Fine Acquisition When the star has been approximately aligned with the focal plane ferrule, move the fold mirror carriage to the Observe position. Switch the STV monitor to input 2. You should see light coming through some/all of the guide fibers corresponding to the science fiber chosen (See Figure 13). If the target is faint, the integration time on this STV may need to be increased in order to see the signal. Using the hand paddle, move the telescope slowly until the light coming through all of the guide fibers equalizes. This indicates that the source is centered, and therefore over the science fiber. This procedure will only work for point-like sources; extended objects can only be coarsely aligned. When the target’s fine alignment has been established, the autoguider may be engaged if necessary. 4.9. Guiding For shorter exposures (< 3 minutes or so), it’s probably most efficient to guide by eye. If the telescope doesn’t track perfectly, you will notice the relative guide fiber light intensities 137 1A 1B 1C 1F 1E 1D 4A 4B 4C 4F 4E 4D Figure 13. View through the Guide Fiber STV. For this picture, the Xenon lamp turned was turned on and the fold mirror carriage was in the “Calib” position. The hexagonal array in the upper left corresponds to the guide fibers around Science Fiber 1 (See Figure 12) while the array in the lower right correspond to Science Fiber 4. change. Manually move the telescope using the hand paddle in the control room to correct the alignment. An auxiliary autoguider is available for use during long exposures. The autoguider is an STV attached to a piggy-backed 8” Meade telescope on the side of the 40” tube. See the 40” manual for instructions on operating that system. Note that the autoguider must be recailbrated every time the telescope is moved significantly in declination. Even while using the autoguider, you should periodically check the guide fiber output to make sure the guiding is working well. If the alignment appears to worsen, turn off the guiding, correct the telescope alignment, and then re-engage the guider. 4.10. Throughput and Exposure times The throughput of the FOBOS + telescope system was estimated by observing the spectrophotometric flux standard star Feige 110 under photometric conditions on UT 2003 November 29. The efficiency curve (Fig. 14) is not constant with wavelength. In particular, the blue response is fairly low, and the red response drops quickly past the peak. Practically, the current setup does not actually provide 2048 pixel spectra; the throughput is low enough at the edges of the spectra so as to render those regions useless. The instrument setup and grating rotation should be set to optimize for the specific wavelength range of interest. At the time that these efficiency data were collected, the telescope’s mirrors had not been aluminized for more than four years. Due to persistent problems with humidity and condensation at the site combined with the advanced age of the mirror coatings, we expect that the telescope’s efficiency has adversely affected the total system efficiency as plotted in Figure 14. Thus, the system performance will likely improve following the next mirror realuminization. With that caveat, estimates of peak signal to noise ratio (S/N) per pixel as a function of exposure time and target V magnitude are presented in Figure 15. 138 Figure 14. Throughput vs. wavelength for the telescope + FOBOS system in the GGSS setup on 2003 November 29. The efficiency of FOBOS alone should be higher because we expect considerable contribution to the reduced efficiency (especially at shorter wavelengths) by the telescope mirrors that had not been aluminized for several years at the time these data were collected. 5. 5.1. Shutting Down Disabling the Vibration Isolator On the ground floor of the observatory, turn the air compressor’s OFF/AUTO switch to the OFF position. Turn the regulator counterclockwise to set the outlet pressure to zero. Detach the isolator’s air tube from the compressor’s air hose in the spectrograph room. To do this, press the the end of the red, plastic connector in while you detach the hoses from one another. Open the regulator on the compressor to depressurize the air tank. Close the regulator when the pressure reaches about 20 psi. Open the drain valve under the air tank to drain accumulated water. When the water has drained, close the drain valve. 5.2. Spectrograph Room Carefully replace the cover on the grating and then the cap on the SLR lens. Fill the dewar using the same procedure outlined in section 3.1.. Open the A/C door and turn the A/C to Medium Cool. Turn on the air cleaner. Turn on the dehumidifier to the halfway point. When the dewar is full, turn off the lights and pull both doors firmly closed behind you. 5.3. Dome Room Replace the telescope cover and send the telescope to zenith (turn off telescope tracking on the electronics rack in the control room first). Turn on the A/C power switch. Set the heat lamp control to “humidistat” and set the humidistat to ∼50%. Power off the spectrograph 139 Figure 15. Lower limit to the predicted peak signal to noise ratio per pixel vs. exposure time for different apparent magnitudes. electronics control box, two STVs, and the autoguider STV. Close the in-tailpiece shutter. Close the exterior doors and dome slit. Turn off the lights and close the door when you leave. 5.4. Control Room Back up your data. If you are at the end of a run, delete your files from the hard drive. After backing up your data, log off of crux. Shut down the autoguider and FOBOS PCs. Power off the TCS PC. Turn off the TV monitors. Send the Focal Plane Module fold mirror carriage to the Calib position. Power down the telescope and tailpiece in the standard way. Leave the FMOEMCS PC and software running. Fill out the observing log. Turn the lights off and close the door when you leave. 6. Troubleshooting Problems? Here are a few suggestions to remedy problems that have occurred so far... • Mirror Carriage gets stuck in the Calib or Acquire position: The fold mirror carriage may occasionally get stuck in either the Calib or Acquire positions. There is a pin on the carriage that triggers various switches to shut off the motor and stop the carriage at a given position. However, the motor occasionally drives the carriage a bit too far, and then the limit switches are engaged, which prevent the motor from running completely. This is to avoid driving the carriage into its hard limits and destroying the motor. To correct the problem, go to the electronics control box on the focal plane module and change the control to Local. Hold down the Limit Override button and manually drive the carriage away from the limit and into the 140 Observe position. Be very careful not to drive the carriage into its hard limits! If the carriage is near the limit on the Calib side, it must be moved toward the West. If its near the limit on the Acquire side, it must be moved toward the East. Don’t forget to switch control back to Remote when you’re finished. If the problem persists, notify observatory staff who may be able to modify the limit switch angles. • Mirror Carriage gets stuck between designated stop positions: This appears to happen infrequently. The cause is unknown, but is suspected to arise from RF interference from other electronics in the dome. If the carriage gets stuck between stop positions, none of the LEDs on the control pad or electronics box will be illuminated. In this case, go to the dome room, switch control on the electronics box to Local, and manually move the carrioage to the West or East until it reaches one of the stop positions and an LED turns on. Then return control to Remote. If this problem persists, notify Jim Barr. • STV shows no image: Chances are that either (1) the telescope’s pointing is off, (2) you need to increase the integration time, (3) you have forgotten to switch the monitor to display the correct camera output, or (4) the mirror carriage is not in the correct position. The first is by far the most likely. The pointing model is imperfect, and we suspect that the toothless friction drive system may slip intermittently. If the pointing is off, go to a nearby bright star and re-initialize the TCS coordinates. If none of the above seem to be the cause of the problem, make sure that the sky has not clouded over and that the telescope is pointed out the dome slit. Finally, check to make sure that the in-tailpiece shutter is open. 7. Data Reduction An IRAF package called FOBOS has been written to assist with data reductions. This is installed on crux at FMO and also locally in the Astronomy Department. The available routines include: • foboscfg — Assists with designing FOBOS configurations for user-specified wavelength ranges. • foboshead — Updates FITS headers with spectrograph configuration information, object names, and IRAF-friendly keywords. • foboslogs — Generates nice postscript observing logs from FITS header information, and optionally adds comments using a user-created input file. Also can generate text observing logs. • fobosmlk — Generates a combined, smoothed flat field from a set of milky flat observations. 141 • fobosinc — Generates a fiber-to-fiber inconsistency file from QTH or daytime sky observations, used to remove the effects of fiber throughput variations. • fobosext — Extracts and identifies wavelength calibration spectra. Extracts, skysubtracts, and wavelength calibrates target spectra. • prep4bandit — Performs some preprocessing necessary for running the BANDIT radial velocity cross-correlation software. Also generates several text files required as inputs for BANDIT. To make full use of foboshead and foboslogs, you’ll want to keep a text comments file while observing. This file should have the following format: the image prefix begins each line, followed by a colon as a field separator, then the object name, followed by a colon and any comments for the file on the same line. When running foboslogs, this file will be interpreted by LATEX, so any special LATEX characters must be “escaped” by a backslash (\). A few lines from an example file follow: ccd1035 ccd1036 ccd1037 ccd1038 ccd1039 : : : : : HD4388 HD4388 HD4388 QTH : NeArXe : RVstd K3III V=7.34 v\_r=-28.3 km/s : : : Neon off after < 1 second Refer to the FOBOS package help files for more detailed information. Peter Frinchaboy has also written a helpful “Cookbook” for FOBOS data reductions. In brief, a typical reduction for a run might look like this: 1. Run foboshead on all FITS files. 2. Run foboslogs on all FITS files. 3. Run ccdproc on the bias frames to trim and overscan-correct. Generate a combined bias frame with zerocombine. 4. Run ccdproc on the milky flat frames to trim, ovserscan-correct, and bias-subtract. 5. Run fobosmlk on the milky flats to create a combined flat field. 6. Run ccdproc on the QTH and/or daytime sky frames, comparison lamp frames, and object frames to trim, overscan-correct, bias-subtract, and flatfield using the combined milky flat. 7. Median combine multiple exposures for each object using imcombine. 8. Extract the QTH and/or Solar spectra using apall. 9. Run fobosinc on the extracted QTH or daytime sky spectra to generate a fiber inconsistency file. 142 10. Run fobosext on the object images to extract, sky-subtract, and wavelength-calibrate them. 11. Run prep4bandit only if you are going to use the MATLAB BANDIT software to determine radial velocities. 8. Neon/Argon/Xenon Spectral Line Identification Charts Figure 16 shows a comparison lamp spectrum taken with the primary setup in the manner described in Section 4.4.. A subset of the identifiable lines is labeled. Most of the Neon lines are considerably stronger than the bulk of the Argon and Xenon lines. However, all will be useful for wavelength calibration provided that the strong lines do not saturate and the weak lines have good singal-to-noise. Note that there are no line identification lists that come with the default IRAF NOAO installation that are appropriate for this instrument. The commonly used idhenear.dat line list will not work well because it contains no Xenon lines, but does contain Helium lines. A special line list, called nearxe ggss.dat has been prepared for the primary FOBOS setup. This was created by using Argon and Neon lines taken from the IRAF henearhres.dat line list and Xenon lines taken from the National Institute of Standards and Technology website. Each of these lists was then used to identify lines in spectra of individual calibration lamps, and those lines that did not appear in the spectra were deleted. nearxe ggss.dat is what remained. Some lines in this list seem to work better than others. In particular, you may choose to delete lines that are blends or closely spaced. This line list has been installed in the IRAF linelist libraries on crux at Fan Mountain, and locally in the Astronomy Department. To use the list with one of the IRAF identify procedures, enter linelists$nearxe ggss.dat for the coordli parameter. Neon is very good for the red part of the primary setup. Argon has fairly good coverage throughout. Xenon is mainly useful in the bluer region. Figure 17 shows a blue Argon + Xenon comparison lamp spectrum (60s exposure at low gain) taken with the “blue grating” (1200@157 in Table 1). The line identifications, listed in the file linelists$arxeb.dat, may be useful for wavelength calibration of blue spectra. 143 Figure 16. Line identifications for Neon-Argon-Xenon spectrum taken with the primary setup (<1 second Neon + 60 seconds Argon and Xenon exposure). Note the different intensity scales for the four panels. 144 Figure 17. Line identifications (file arxeb.dat) for Argon-Xenon spectrum taken with the blue grating (60s exposure). 145 146 Chapter 13 The Santa Barbara Instruments ST-8/ST-1001E CCD Cameras 147 148 Santa Barbara Instruments ST-8/ST-1001E CCD Camera (Rev. August 06, 2007) General Information You will be using the ST-8 camera either as an imaging camera, or as the detector for the Optomechanics 10C Spectrograph. In both cases, set up and operation of the CCD camera are identical. ST–8 Specifications: Camera: Santa Barbara Instruments Group ST–8 PC operated CCD Chip Type: Eastman Kodak KAF–1600; 2 phase, front illuminated chip Format: 1530 × 1020 pixels 9 µm square Spectral Range: Sensitive from 4000 – 11000 ˚ A Read Noise: 15 electrons/pixel RMS Cooling: On–board thermoelectric cooler You will be using the ST–1001E as an imaging camera. ST–1001E Specifications: Camera: Santa Barbara Instruments Group ST–1001E PC operated CCD Chip Type: Eastman Kodak KAF–1001E; 2 phase, front illuminated chip Format: 1024 × 1024 pixels 24 µm square Spectral Range: Sensitive from 4000 – 11000 ˚ A Read Noise: 17 electrons/pixel RMS Cooling: On–board thermoelectric cooler This manual is designed to take you through the setup and operation of the CCD cameras step-by-step so that you can perform your laboratory without having to rely heavily on a Teaching Assistant. The CCD is delicate, however, so if you are uncertain about how to do something please ask the T.A. for help before trying to do it yourself. Throughout this manual, it is assumed that you already have a general understanding of the use of CCD cameras. Appended to the end of this manual is a list of references to literature on the design and use of CCDs if you need additional information not provided here. 149 1. CCD Set Up When you arrive at McCormick Observatory, the CCD (or spectrograph) mounting will already be connected to the tail end of the 26” refractor. If it is not, only the T.A. is authorized to change the tailpiece. Do not attempt to do this on your own. With the tailpiece mounted on the telescope, and the CCD mounted to the tailpiece, set up is actually quite simple. The CCD needs to be connected to the control computer (an IBM compatible PC), which requires the following steps: 1. Carefully roll PC cart from observer’s room to dome. 2. Plug powerstrip on PC cart into long orange extension cord. 3. Plug extension cord into outlet on East side of 26” pier. 4. Connect the male end of the ribbon cable into the parallel port on the PC. Connect the female end of the ribbon cable to the parallel port on the CCD head. 5. Connect the 5–pin power cable from the CCD power supply to the CCD head. Plug the power supply into the power strip on the PC cart. If everything is connected properly and the unit now has power, the red LED on the rear of the CCD head will glow and the fan will begin spinning. 6. Plug the PC and the PC monitor into the power strip on the PC cart. Start the PC by pressing the power button. A PC is required to control the CCD’s various functions. There are two different software packages installed on the PC which can control the CCD, CCDOPS and SkyPro. Both programs are essentially the same, the main difference being CCDOPS is run from DOS and SkyPro is run from Windows. The following sections of the manual are written assuming that you will be using CCDOPS to control the CCD. However, SkyPro is very similar to CCDOPS, and if you prefer to use the Windows environment, you can use SkyPro. To start CCDOPS do the following: 1. In the FILE menu select the “Exit Windows” option. 2. from the DOS prompt, type: cd CCDOPS. 3. from the DOS prompt, type: CCDOPS. You should now see the CCDOPS software displayed on the monitor. The next section will describe how to control the camera with this software. 150 2. CCD Operation with CCDOPS This section of the manual covers the initialization, use, and shutdown of the CCD camera with the CCDOPS software. If you are using the SkyPro package, the steps are similar, however, location of the commands may not be in the same menus as in CCDOPS. CCDOPS is DOS-based software, so to maneuver through the menus you will use the arrow keys. To select a menu item, press return when you have highlighted it. You can also use the mouse to select menu items as you would in Windows. CCD Initialization Prior to observing, there are several steps you should take to initialize the CCD Camera. First, you need to establish communication from the CCD head to the computer. To do this, simply select Establish COM link in the Camera menu. When the program is started, it includes a status area on the bottom of the screen. In the camera section of the status area it should say “Link:Not Found” when you start CCDOPS. After selecting Establish COM link, however, this should change to indicate that a link has been established through port LPT1 to the ST-8. Once this link has been established, you can begin using the CCD Camera. Next, you should choose Setup from the Camera menu to set the CCD operating temperature, resolution, and dark frame use. To minimize dark current, you want the CCD temperature to be as low as possible. The CCD has an on–board thermoelectric cooler which can quickly cool the chip to low temperature. After choosing Setup in the Camera menu, type in a setpoint where indicated. This value should be between 0◦ and -10◦ Celsius. Once you’ve entered the setpoint, switch the temperature regulation to active. The current temperature is displayed at the bottom of the CCDOPS screen. You can begin exposing the CCD when the temperature nears your setpoint (should be within a few minutes). In the same Setup box, you can also choose the resolution of the camera. There are three resolution levels, High, Medium, or Low. In high resolution mode, the chip reads out all pixels. In medium, the chip reads out bins of 2x2 pixels, and in low, the chip reads out bins of 3x3 pixels. High resolution mode is best, since you keep the most information when you read all pixels. The drawback to high resolution is that the chip read time is significantly longer than in medium or low resolution mode. Therefore, use high resolution on program objects, and use medium or low on focus frames, first test frames of program objects, and other throwaway exposures. Finally, you can select whether or not you would like to take dark frames. Since this CCD is only thermoelectrically cooled to just below 0◦ Celsius, it has a significant amount of dark current. Subtracting a dark frame and from your real exposure will remove fixed pattern noise from the variable dark current and bias level of the chip. CCDOPS can be set to automatically take and subtract a dark frame from your real frame before displaying. To do this, set dark frame to Also in the Setup window. If you will be taking multiple exposures of the same duration and at the same temperature then you can also set Reuse Darks to Yes. Note that a dark frame must be the same length as your program frame. Therefore, a 15 min. exposure with a dark frame will take more than 30 minutes including readout time. The reuse dark option will significantly reduce observing time for multiple long exposures. 151 Note that the CCD Camera Setup can be changed at any time during the night. You can switch resolution, dark frame use, and temperature (although there is really no need to change the temperature) whenever you wish. CCD Operation Using the ST-8 CCD with the CCDOPS software is quite easy. While the software has many sophisticated options, you can obtain high quality exposures very simply. There is no cookbook list of numbered steps you can follow, since how you use the camera will depend very much on the observing program you are performing. However, there are several steps common to all programs which will be outlined below. The most important thing to do before beginning your observations is to focus the telescope as best you can. To do this, select the Focus command in the Camera menu. The Focus command tells the CCD to take a series of frames continuously, allowing you to adjust the focus of the telescope in between each one. Of course, to focus the telescope, you need to have an object to focus on, so before beginning to expose the chip, point the 26” at a fairly bright star (say 9th to 12th magnitude). In the Focus window, set the CCD to “Planet” mode. Then set the exposure delay to give you enough time to adjust the telescope focus between exposures (for the 26”, you will probably need at least 20-30 seconds). Finally, set the exposure time for each frame long enough to integrate over changes in seeing, ten seconds or so is enough for a bright star. When you hit enter, the CCD Camera will begin a sequence of exposures. Planet mode tells the camera to first take a full frame exposure. Then, after reading this exposure out and displaying it to the screen, you will see a white box appear in your image which is smaller than the chip. You can place this white box anywhere in the image using the arrow keys. After putting the box around the star you are using to focus, hit the return key twice. This will instruct the chip to only read out the portion of the chip included in the box. Chip readout times will therefore be reduced and you can focus the telescope quickly. Once you have used the “locate” box to select your focus object, crank the focus of the 26” 1–2 cranks between focus exposures. If for some reason you lose the star from the “locate” box, you can restart Planet mode without exiting your current Focus run. To do this, simply select Planet from the menu which appears in the upper left hand corner when a focus image is displayed. This will make your next frame full size again so you can recenter your focus star. There is a straightforward method for determining the focus of the telescope quite accurately. Begin your Focus exposure set with the telescope way out of focus in one direction. As the frames progress, slowly move the focus in or out so the stellar image begins to narrow on the chip. To find the focus, continue doing this until you’ve gone past the focal point, and the stellar image has begun to widen again. Once you’re sure you are past the focal point, simply go back in the other direction until you have the image as narrow as possible. To further improve the accuracy, you can use the peak pixel value of the image. The number which is displayed to the left of the image window gives you the value of the pixel in the displayed frame which has registered the most counts. As you achieve better and better focus, the light from a star is concentrated into a smaller area. Therefore, the value of the central pixel will increase as you achieve better focus. So, while you are focusing the stellar image and minimizing its spatial extent, look for the maximum pixel value. When the image is at its narrowest, and the pixel value is at its highest, you have achieved focus. 152 After achieving focus, the use of the CCD Camera will depend on your particular observing program. The rest of this section will describe how to take a standard CCD exposure, which is common to all programs. To take an exposure, select the Grab command from the Camera menu. The Grab command is very similar to the Focus command, except it takes only 1 exposure instead of a series. Simply select your integration time, and press Return and the exposure will begin. Remember, the resolution (high, medium or low) and use of dark frames for this exposure is set in the Setup option of the Camera menu. You can change those options between each exposure to fit your observing needs. In some cases, you may wish to use SBIG’s “Track and Accumulate” software as an alternative to simply using the Grab command. To use this option, select Track and Accumulate under the Track menu in CCDOPS. The Track and Accumulate option allows you to take several shorter exposures of your program object rather than one long exposure. The software will then co-register and co-add the multiple short exposures, leaving you with a single, stacked image. Using this software option will require you to set the following parameters: Snapshot Time: Integration time for each exposure (60 – 120 sec is probably best). Number of Snapshots: Number of snapshots to take and then co–add. Dark Interval: Set this to “Series” and then the same dark image will be used for all of the individual frames. Track Mode: Set this to “Align” to tell the software to co–register the images. The other parameters for Track and Accumulate can be left with their default values. After you begin the Track and Accumulate process, the first exposure will begin. Like the Focus command in “Planet” mode, your image will be displayed with the “locate” box displayed. You now need to move the locate box until it encloses a star which can be used for guiding. After subsequent exposures, the software will use the pixel position offset for your chosen guide star to perform the co–registration. For this reason, you should select a fairly bright star away from the edges of the chip as your guide star. CCD Shutdown When you are finished with your observing program, you will need to shutdown the CCD and computer system. First, select Shutdown from the Camera menu. This terminates the communications link from the CCD to the computer. Next, select Exit from the File menu. This will return you to the DOS prompt. You can now turn the PC off by pressing the Power button. Now simply perform the setup in reverse. Remove the power cable from the CCD head and roll it up. Remove the ribbon cable from the CCD head and roll it up. Unplug all plugs and store them on the cart as you found them when you arrived. Roll the cart slowly into the observer’s room for storage. 153 CCDOPS miscellanea As mentioned above, CCDOPS contains many more options than those described in this manual. You will probably not need to use any of them other than those described above, however. If you are performing a lab which does require some other option, either the TA or the lab manual will describe how to use it. This last section will go over a few final details about using CCDOPS. At any time, hitting the Esc key on the keyboard exits what you are doing. So when you are finished with your focus run, or if you want to abort a long exposure because of a problem with the telescope, etc., simply hit Esc. Also, after your exposure taken with Grab has finished and has been displayed to the screen, Esc gets you back to the main CCDOPS screen. The current image is kept in the image buffer until it is saved to disk or another exposure is taken. So after your image has been displayed and you have hit Esc, you can continue to redisplay it until you save the image or replace it with a new one. To redisplay it, select Image from the Display menu. This option also allows you to change the display parameters so that you can enhance faint detail or only display the brightest portions of the image. To change the display parameters, simply type in a new background and range where indicated in the Image window. In addition to changing the display parameters with Image, you can also get some useful information about your image. Set the “Display Mode” in the Image window to “Analysis” after you have selected Image from the Display menu. You will notice a menu of options now available in the upper left hand corner of the display. If you select “X-hairs” (or simply type X), a set of crosshairs will appear on the display. The box in the upper left hand corner will now display the pixel position and value for the current pixel. Finally, you will want to save your images to disk so that you can retrieve them later for data reduction and analysis. If you will be porting the images to the department’s UNIX Workstations for analysis in IRAF or IDL, you will want to save your images in the FITS (Flexible Image Transport System) format. To do this, simply select Save in the File menu. Type in a unique name for your image and then set the “Type” to FITS. A second window will appear, titled “Save FITS Image”. In this window, set “Bits per pixel” to 16, and type in any comments you would like in the fields indicated (Telescope, Observer, Object, Comments). When you hit Return, the current image will be saved to disk. 154 Chapter 14 The OptoMechanics Model 10C Spectrograph 155 156 OptoMechanics Model 10C Spectrograph (Rev. August 09, 2011) 1. General Information Certain laboratory exercises will require you to use the Spectrograph and CCD together instead of simply doing straight CCD imaging. The CCD setup and operation are identical to that described in the first part of this manual. This section is designed to take you through the setup and operation of the spectrograph so that you can perform your laboratory without having to rely heavily on help from a Teaching Assistant. Like the CCD, the spectrograph is a delicate instrument and should be treated with care. The optical elements, in particular, are very expensive (as is the CCD). As with all delicate equipment, NEVER force any moving part beyond reasonable and expected resistance. Never move the telescope by pushing on the spectrograph or CCD, and never lean or support yourself by holding onto this equipment. Never, NEVER, touch any optical element. Oils from your skin will permanently embed into glass surfaces and optical coatings. It is preferable to leave small amounts of dust on optical surfaces rather than risk scratching or marring the surfaces with attempts at cleaning. If you are uncertain about how to operate any aspect of the spectrograph, please consult the T.A. for help. THINK BEFORE DOING. Just as in the CCD section, this section will assume you have a general understanding of spectroscopy. You will find information on spectroscopy in the references listed in an appendix at the end of this manual if you need more information not provided here. 2. 2.1. Use of the Spectrograph Instrument Design Figure 1 gives a view of the spectrograph and mounting at the tail of the 26” Clark refractor. An external view of the grating assembly including the dial can be seen in Figure 2. Figure 3 shows a layout of the internal optical design of the instrument. A sample spectral image of a star and comparison sources is in Figure 4. The major elements of the instrument are: Instrument Rotation Ring: This allows rotation of the slit angle on the sky. At present, there are detents every 15 degrees of rotation, but random angles are also possible. Do not rotate slit position angle without TA assistance. The default position angle is 90 degrees. 157 Focal Reducer: The first optical element of the spectrograph is a transfer lens. This lens serves to speed up the (rather slow) f/14.9 refractor telescope beam to f/10. Slit Assembly: At present, there are two slits available with spectrograph, a 50µm width slit which is equivalent to ∼ 1.5 arcseconds (calculated with f/10 and 26” aperture), and a 100 mm width slit which is equivalent to ∼ 3.1 arcseconds. You can tell which slit is in the beam by the color of the round knob (see Figure 1): black is the 50µm and silver is the 100µm. The “slit” is actually a set of three slits end-to-end. Your sky source will be imaged onto the central slit, which is 1.5 mm = 46.8 arcseconds in length. The two side slits are fed light from the comparison source via fiber optic cables for simultaneous recording of astronomical and comparison source spectra. Figure 1. The Spectrograph and Mounting on the 26-inch Clark Refractor. Comparison Source: At present there are two available comparison lamps, mercury and neon/argon. In general, you will want to use both sources, although certain spectral regions are devoid of lines from one or the other. If this is the case for your particular wavelength set-up you can extend lamp life by using only the source needed for your work. The lamps have been intensity balanced to achieve approximately equal line intensities; however, these lamps do have a limited lifetime which results in gradual dimming. If you should notice peculiar line intensity ratios between the mercury and neon for the same exposure time, notify the TA. In this spirit, please DO NOT LEAVE 158 Figure 2. This image includes the grating knob, the counter displaying degrees of tilt angle (here, 28 degrees), as well as the lock to hold the grating at the specified angle. THE LAMPS ON for more than the time required to make your comparison spectrum (typically ∼ 1 − 5 seconds). An atlas of the Hg-Ne/Ar source lines is given in Appendix A. Guide Eyepiece: At present, acquiring objects and guiding the telescope is done manually through the guiding eyepiece assembly. The image plane of the telescope (when in focus) is on the slit “jaws”; an aluminized mirror surface into which the slit holes are cut. Thus, through the guide optics you observe that part of your source which does not fall through the slit. Your goal in guiding the instrument is to ensure that as much of your source flux falls through the slit as possible, and in general at the same place along the slit. Collimator: The collimator is a 225 mm focal length mirror which converts the converging telescope beam into a collimated beam. Grating: Four gratings are available with this spectrograph with rulings of 240, 400, 600 and 1200 grooves per mm (at present, we do not have the 400 line grating). All are blazed (yield maximum reflection) near 5000˚ A. When used in first order, these gratings yield spectral resolutions of 295, 180, 120, and 60 ˚ A/mm. Note that the ST8-CCD has pixels of size 9µm (at high resolution; when binned, the pixel size changes accordingly), a limitation which must be included in any calculation of the true resolution. You may NOT change gratings yourself. In general the grating needed for your experiment will be in place before you arrive at the Observatory. If this is not the case, please ask the TA for any changes. In order to remove the grating: 159 1. Set the tile angle to 35 degrees. 2. Unscrew (but don’t remove) the 3 recessed 4-40 sockethead screws that fasten the grating assembly to the housing. 3. Carefully withdraw assembly from housing. UNCOVERED AND FACING CAMERA. NOTE THAT GRATING IS 4. Immediately and carefully install cover on grating cell, to protect grating during subsequent handling and storage. 5. Turn over assembly and remove the two 8-32 sockethead screws holding the grating cell to the assembly. 6. Install new grating cell and remove its cover just before replacing the assembly back into housing (STORE COVER IN SAFE PLACE). The spectral region delivered from the grating to the detector is determined by the grating tilt, controlled by the lockable knob with counter (Figure 2). The counter displays degrees of tilt angle (always approach final tilt setting from lower values for reproducible results). Zero tilt angle is when the grating acts as a normal mirror. Tables of central wavelength delivered as a function of grating tilt are given in Appendix B. Note that the knob is quite loose until locked, so that if you do not lock the knob, you run the high risk of your spectral region shifting with time and telescope angle. In principle, these gratings can be used in other than first order; in practice, both the refracting optics of the telescope as well as the CCD detector have limited spectral range (centered on the yellow part of the spectrum) which limit access to other orders. For this reason, the spectrograph does not presently have capability for adding order blocking filters. However, it is good practice when working with a spectrograph to consider the possibility of spectral contamination by higher orders. Camera: The camera for this spectrograph is a 135 mm focal length Nikon lens for a 35 mm camera. It is focused in the usual way a camera lens is focused, by rotation of the knurled outer ring. Detector: The standard detector for the spectrograph is the ST8 CCD, although other detectors (e.g., a 35-mm film camera) may also be used. Do not attempt to remove the CCD without TA assistance. With spectrographs on large telescopes, the first operation of an observer is to ensure that the detector is rotated so that the spectrum is aligned straight along CCD rows. However, as this is a delicate operation with the 10C, only the T.A. is allowed to perform this operation, which will be accomplished before you arrive. However, you should check the detector alignment by checking the placement of the same line on the pairs of comparison source on either side of your image. DURING YOUR WORK WITH THE SPECTROGRAPH, YOU ARE ALLOWED TO MANIPULATE THE FOLLOWING WITHOUT T.A. ASSISTANCE: • Telescope 160 • Telescope focus • Guider eyepiece focus • Camera focus • Grating tilt • Comparison source power • CCD camera YOU MUST NOT DO THE FOLLOWING OPERATIONS WITHOUT TA OR FACULTY ASSISTANCE: • Change slits • Change gratings • Change comparison sources • Rotate instrument position angle • Rotate CCD on spectrograph 2.2. Spectrograph Set Up Generally, when you arrive at McCormick Observatory, the Spectrograph mounting will already be mounted to the tail end of the 26” refractor, with a specific grating and slit appropriate to your experiment, and the ST-8 CCD connected to the camera optics of the Spectrograph. The equipment is generally protected with the silver cover, which you may need to remove. In addition to the CCD setup as described in section 1.1 of this manual, there is only 1 additional step required for preparing the spectrograph. The spectrograph has two comparison lamps in a black housing connected to the main (blue) portion of the spectrograph. These lamps need to be plugged in to the powerstrip on the PC cart with the extension cord provided. You do not need to turn on the comparison lamps until they are needed, so for now simply plug in the lamps but leave them off. 161 Figure 3. The Optical Design of the Spectrograph. 162 2.3. Spectrograph Operation The ST-8 CCD camera is usually used as the instrument detector for the 10C Spectrograph. Familiarize yourself thoroughly with operating this device before proceeding. Before you start observing, you need to initialize the ST-8 using the MaxIm DL imaging software . Operation of the CCD is no different when using the spectrograph than if you were doing straight CCD imaging. However, since with spectroscopy you will often be working closer to the background levels of the CCD, it is important to make sure that the CCD temperature is cold (at least -10 C) and stable throughout your observations. Using the spectrograph is slightly more complicated than straight CCD imaging, and you should follow the steps below. In some cases, you may need to iterate between steps. 2.4. Slit and Grating Verify that you have the appropriate slit and grating for your experiment (see above). Check the position angle (PA) of the slit on the sky and see if it matches your needs. In general, PA = 90 degrees (East-West) is recommended. If the position angle needs to be rotated, contact the TA. 2.5. Camera Rotation It makes sense, whenever possible, to align the dispersion axis of the spectral images along the rows of the CCD (i.e., along the long dimension). You obtain about 50% more spectral coverage on one image if you place the dispersion along the long axis of the CCD than along the short. If the CCD is not oriented in this way, discuss the matter with the TA. The image in Figure 4 was made with the dispersion in the less favorable CCD orientation. Take a short exposure with a comparison source on, and verify – by comparing the position of Hg-Ne/Ar lines on each side of the image – that the CCD detector is aligned with the spectrograph (to within a pixel or two on either side). If the two comparison spectra are not well aligned (parallel), notify the T.A. Check also that the camera is tightly held onto the spectrograph; if the camera is loose, you may get unwanted rotations introduced into your images as the telescope moves around. 2.6. Spectral Range Based on the goals of your experiment, you should have a clear idea of the spectral region you require. Based on the grating dispersion and the fact that the ST-8 has 1530 pixels of 9µm size along the dispersion axis, you can calculate your approximate accessible spectral range. You will want to vary the central wavelength so that that available range contains your desired astrophysical spectral features. For example, if you are observing planetary nebulae, which have the prominent [O III] emission line doublet at λ = (4959, 5007), you will want to have the central wavelength set to ∼ 5000˚ A. Appendix B lists the appropriate angles and 163 Figure 4. Example spectrum of a V = 5 M star taken with the 240 line mm−1 grating centered at about 5000˚ A. Exposure time was 45 seconds for the star and 1 second for the calibration lamps; with 2x2 binning, the maximum flux on the red end was 12,500 ADU. However, due to the effects of chromatic aberration from the 26-inch lens and the focal reducer, the image of the star fans out as it goes out of focus in the blue. As a consequence of this and the transmission properties of the system, the spectrum quickly drops in level to 0 ADU. wavelengths for a given grating. The spectrum in Figure 4 is with the low resolution, 240 A. line mm−1 grating and centered near 5000˚ Tilting the grating determines the central wavelength of the resulting spectrum. To set the grating tilt angle, you simply unlock and then turn the knob on the side of the spectrograph housing. It has an “odometer”–like counter next to the knob which tells you the tilt angle in degrees. To unlock the knob, slide the black lock underneath the knob to the left. Then, twist the knob so the meter reads the angle required. When it is set, slide the lock back to the right. When setting the angle by twisting the knob, you will notice there is a significant amount of backlash. Therefore, you should always approach the desired value from a lower value of the angle. In this way, you are most likely to match your setup should you need to return to it in the future. Because the tilt knob turns so freely, please take care to slowly move the grating. 164 2.7. Focusing the Spectrograph There are two focus operations involved in the use of any spectrograph: (1) You must first focus the exit beam from the grating onto the detector, and (2) you must focus the entrance beam from the telescope into the spectrograph onto the image plane of the slit. Astronomical spectrographs require one additional focus operation, which is that of the guiding optics on the image plane of the reflecting slit surface. Before taking a spectrum of your program objects, you will need to carry out these three focus operations. Remember that your spectrograph is most efficient when both the telescope and camera are in best focus, as this concentrates light from your source onto the smallest number of CCD pixels (increasing signal–to–noise). In addition, the best spectral resolution with any particular grating/slit setup is achieved when the camera is in best focus. First, you must focus the spectrum on the CCD using the calibration lamps. This is done by turning the camera lens which is connected to the CCD head just as if you were focusing a normal 35 mm camera. You will also need to take short 1-3 second exposures. You can evaluate the focus by using MaxIm DL to extract vertical plots of the calibration spectra. First, turn on one of the calibration lamps to use as the spectrum for focusing (we recommend the Ne lamp because of the numerous amount of available lines). Open the ‘Focus’ tab in the ‘CCD Control’ window and take a short exposure of the entire CCD (make sure ‘Continuous’ is not checked). Place the cursor as a thin box traversing a close line doublet on the calibration source spectrum to select a subframe. Check the ‘Continuous’ option and click ‘Start Focus’ to run the feed at 1-3 second exposures. With the ‘Line Profile’ tool, place a vertical line cut across the doublet (which should appear as a double humped curve in the plot). Begin with the camera lens turned to one limit and slowly adjust the camera lens focus by twisting the barrel of the lens. Look for the point in the graph at which the lines in the doublet become the most distinct from one another. This should coincide with the point at which the peak flux in the lines is greatest. At first, you may require large turns to get the focus “in the ballpark”; but when closing in on the best focus, small turns of the lens yield noticeable results. You may need to iterate back and forth to find the very best position. The best focus is achieved when spectral lines are narrowest, when the maximum count value is the highest, and when pairs of lines appear most clearly separated. It is important to remember that lenses suffer from chromatic aberration. Because the system you are using has three lenses (telescope, focal reducer and camera) it may not be possible to have your entire spectrum in focus at the same time. Figures 4 & 5 shows what happens when chromatic aberration affects a spectrum. Based on your experimental goals, you will have to decide where you want your best focus. Note that simply focusing on the center of the CCD chip means that the majority of the spectrum will not be in best focus. If you are interesting in achieving the best possible focus along the entire dispersion, it is often best to focus at about 1/4 of the way from either end. Next focus the guide eyepiece on the slit. First put an eyepiece in the black tube projecting from the side of the spectrograph if there is not one already there. Depending on the nature of your source (bright versus dim, compact versus extended), you may find that you need a higher or lower magnification eyepiece for optimal guiding. 165 Turn on one of the comparison lamps using the toggle switches on the lamp housing. Twist the eyepiece in and out of the tube until the slit (the black lines visible against the comparison lamps) is in sharpest focus. Do not be confused by the comparison lamps; when the slit is in focus in the eyepiece, the comparison lamps will be out of focus. Finally, you will need to focus the telescope image on the slit. To do this, first point the 26” at a bright star or planet. If you are pointed correctly, you will see your object in the spectrograph eyepiece. Note that you will see the silhouettes of the comparison source fiber optic assemblies against the (brighter) night sky. With your bright object in the center of the field of the spectrograph eyepiece, crank the telescope focus until the image is in focus. The most accurate way to focus your object is to go through the focus and then go back slowly until you have the image as small as possible. Because the entrance beam to the slit is fairly slow (about f/10 after the focal reducer), it may be hard to tell when you have achieved best focus. In this case, you should take a series of CCD images with a bright star centered on the slit. Take exposures sufficiently long to integrate over the seeing (i.e., more than a few seconds), but short enough that your stellar spectrum is not saturated. At first, you may want to test the focus once every three or four complete cranks of the telescope focus, until you can zero in on the approximate region of best focus. Then do another focus series, with steps of 2 cranks in between, and so on. Depending on the seeing, the smallest focus difference you may be able to discriminate may be 1-2 cranks. Best focus is achieved when the spectrum is narrowest or has the highest flux in the central pixels. 2.8. Observing with the Spectrograph Once you have set the focus of all three components of the spectrograph system, you are ready to begin observing your program objects. First point the telescope at the object you wish to observe. Once it is aligned in the finder, it should be visible through the guide eyepiece on the spectrograph. You will then need to adjust finely the position of the object so that it is bisected by the slit. In some cases (e.g., to observe two nearby objects simultaneously, or to align along the major axis of a galaxy or nebula) you may need or desire the slit to be in another orientation on the sky. Ask the T.A. to rotate the spectrograph position angle for you. If there are no other considerations, we recommend using the spectrograph in a position angle of 90 degrees (i.e., an East-West slit). The slow telescope motion is much easier to control in the declination than in the right ascension direction, so it easier to place objects on the slit if the slit is at PA = 90 degrees. To place an object on the slit in this orientation, first roughly center the object in right ascension above or below the slit. Then lower or raise the object onto the slit with the declination slow motion. When the object is aligned with the slit you are nearly ready to observe. Remember that you must make sure the object remains on the slit in the same position throughout the entire exposure to maximize efficiency. It is a good idea, therefore, to guide the exposure throughout the integration. Your goal in guiding is to ensure that as much object flux falls through the slit as possible, and in the same place along the slit. Thus, you will be guiding on the edges of objects – those parts that do not fall through the slit. Here, again, we have 166 found using PA=90 degrees to be an advantage. The 26-inch seems to track fairly well in right ascension over the course of several minutes, and is even more steady in declination. Thus, it makes sense to keep the narrow dimension of the slit in the north-south direction, where there will be the smallest telescope movement (though refraction will come into play for long exposures at high zenith angle). At PA=90 degrees, any mistracking of the telescope in hour angle will be along the slit and, while not optimally concentrating flux in the fewest number of pixels, at least no flux is lost in this situation. Take exposures using your favorite software package such as MaxIm DL. You will need to compare the spectrum of your object to the Hg-Ne/Ar comparison lamps for wavelength calibration purposes. Therefore you need to turn on the comparison lamps briefly during your exposure. Be sure not to leave them on too long, or they will saturate and you will not be able to accurately wavelength calibrate your spectrum. You may also risk ruining your object spectrum from charge leakage by supersaturated pixels. You will also shorten the lifetime of the comparison lamps. We have found that with 2x2 on-chip binning of the CCD, comparison lamp exposures of about 1 second are fine with the lowest resolution grating (240 lines mm−1 ). Keep in mind that the chip saturates at 65,535 ADU, and both your object spectrum and calibration lines must be below this to be useful. As a guide, with 2x2 on-chip binning and the 240 lines mm−1 grating, magnitude 4-5 stars will saturate the chip in about a minute. During your observations take care that the instrument will not run into anything (pier, ladder, fellow students) and be mindful of all cables. When you are finished observing, follow the usual CCD shutdown procedures. The only additional step necessary for shutting down the spectrograph is unplugging the comparison lamps, rolling up the cord, and putting the cover on the spectrograph. 3. 3.1. Reduction of Spectrographic Data Preparation Once you have finished observing and are ready to analyze the data, you can log into one the Department of Astronomy’s Astro 3130 Windows XP workstations (Room 233). See the the Computing Handbook (http://www.astro.virginia.edu/∼hbp4c/computing/handbook/Computing.pdf) for more information. You will be able to use the MaxIm DL and/or MIRA software package (whichever you prefer) to reduce and analyze your CCD data. The astro3130 account should already be set up to run these programs. Contact your TA if this is not the case. First it is important to make a directory for the raw images (e.g., “raw”) that were taken at the telescope and a separate directory for all your processed images (e.g., “proc”). This will prevent you from overwriting your raw data, which should be kept as is. These subdirectories can be made in your group directory on the astro3130 network drive (Orion). You should start by making copies of the raw images and putting them in the “proc” directory. 167 3.2. MaxIM DL In order to dark subtract an image, have your image frame open along with the corresponding dark frame of equal integration time. Open the Pixel Math command via the Process menu. Set the following options: • Image A: Select your image frame file from the drop down list. • Image B: Select your dark frame file from the drop down list. • Scale Factor %: Make sure both of these are set to 100. • Operation: Subtract. • Add Constant: 0. Hit OK and save the new image under a file that indicates it has been dark subtracted (ie. “Image sub.fits”). With the Line Profile tool, take the mean over many columns by using a vertical box selection method in order to increase your signal-to-noise and to overcome the differences in focus with wavelength. After choosing the Vertical Box and Mean option in the Line Profile window, draw a selection box down the length of the spectrum that has a width approximately equal to the size of the out-of-focus flared portion. Click the Export button to output the resulting plot to a .csv file to be opened with Microsoft Excel or some other spreadsheet program. Using the comparison lamp spectra as a guide (Appendix A), place a wavelength scale on each spectrum. 3.3. MIRA Have two images open in MIRA, the combined dark image and the object image. Open each image separately (i.e., not as an Image Set). Make the object image window the ‘active’ window. This is done by clicking on that image. Under Process\Math, select ‘Image Arithmetic’. Under Image, choose the frame that contains the spectrum you want to analyze, choose ‘Subtract’ as the Operation, and choose your dark frame as your Operand Image. Click Process and then save the new object image using ‘Save as’; select a new name for the image so as not to overwrite the old image (ie. “Image sub.fits”). Repeat this same process for all of your observations. 168 4. Ne–Hg/Ar Comparison Sources Wavelength source: National Institute of Standards and Technology (NIST). For reference, H-Alpha and H-Beta occur at 6563 and 4861 Angstroms, respectively. Figure 5. A composite of the wavelength calibration spectra. The left spectrum corresponds to the Neon calibration lamp, while the right shows the Mercury/Argon calibration spectrum (Argon lines are the broad, dark lines above 7000 Angstroms). The middle strip contains the combination both lamps. These spectra were taken using the low resolution 240g/mm grating. 169 5. Central Wavelength vs. Grating Tilt Wavelength (˚ A) 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000 Wavelength (˚ A) 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000 240 Tilt (◦ ) 2.60 3.00 3.35 3.70 4.10 4.45 4.85 5.20 5.60 5.95 6.35 6.70 7.10 7.45 600 Tilt (◦ ) 6.50 7.45 8.40 9.35 10.30 11.25 12.20 13.15 14.10 15.05 16.00 17.00 17.95 18.95 g/mm Grating Dispersion (˚ A/mm) 290.2 290.9 291.6 292.2 292.8 293.5 294.1 294.7 295.3 295.9 296.4 297.0 297.5 298.1 g/mm Grating Dispersion (˚ A/mm) 118.7 119.2 119.7 120.2 120.7 121.1 121.5 121.8 122.1 122.4 122.7 122.9 123.1 123.2 170 400 g/mm Grating Tilt (◦ ) Dispersion (˚ A/mm) 4.35 176.0 5.00 176.6 5.60 177.2 6.20 177.8 6.85 178.3 7.45 178.8 8.10 179.4 8.70 179.9 9.35 180.3 9.95 180.8 10.60 181.2 11.25 181.6 11.85 182.0 12.50 182.4 1200 g/mm Grating Tilt (◦ ) Dispersion (˚ A/mm) 13.15 60.9 15.05 61.2 17.00 61.4 18.95 61.6 20.90 61.7 22.95 61.7 24.95 61.7 27.05 61.5 29.15 61.3 31.30 61.0 33.50 60.6 35.75 60.1 38.10 59.5 40.50 58.7 6. References on CCD Imaging and Spectroscopy The preceding sections of the manual all assume a general knowledge of CCD Imaging and Spectroscopy. Prior to performing a CCD or Spectrograph laboratory exercise you should have received instruction on these instruments in class. If you wish to read about these subjects in more detail, however, the following list of references may be useful: • Fillipenko, A. V. 1982, PASP, 94, 715 • Kitchin, C. R., 1991, Astrophysical Techniques (New York: Adam Hilger) Sections 1 &4 • L´ena, P., 1988, Observational Astrophysics (Berlin: Springer) Sections 5 & 7 7. File Transfer to UNIX Workstations After your observations have been completed, you will want to analyze your new data. You will most likely be using the UNIX based astronomical data reduction software IRAF (Image Reduction and Analysis Facility) or IDL (Interactive Data Language). Both of these packages will read FITS (Flexible Image Transport System) images, so it is imperative that when you save your images on the PC, to save them as FITS files and not TIFF or PC compressed/uncompressed files. To use IRAF or IDL to analyze your images, you first need to transfer the files to the Astronomy Department’s UNIX workstation cluster. To do this requires the following steps: 1. Wheel the PC cart to the “museum area” of the observatory. 2. Connect the co–ax ethernet cable to the port on the back of the PC. 3. Boot up the computer. 4. If the computer is not already at the DOS prompt, exit Windows. 5. At the Dos prompt, type: ftp astsun.astro.virginia.edu 6. Login to either your account, or the class account (e.g. astr3130) on astsun. 7. cd to the directory on astsun where you would like the images to be stored. 8. type: lcd \ccdops to get to the CCDOPS directory on the PC. 9. type: binary to ensure your images are transfered in the proper format. 10. type: put filename replacing filename with the name of the image you have stored on the PC’s disk. 171 11. repeat the item 7 until you have transferred all of your images. 12. type: bye to exit ftp. With several classes using the PC for CCD operation, the disk will eventually fill up. You will therefore need to eventually delete some of your images from the PC disk after you have transferred them to the UNIX machines. However, DO NOT delete your images from the PC until you have tested them on the UNIX machines to make sure they were transferred properly. 8. 8.1. Reduction of Spectrographic Data with IRAF Viewing and Extracting Spectra Once your spectral image is transferred to the Unix environment (Appendix D: File Transfer to UNIX Workstations), you can begin sophisticated analysis. If you are already familiar with the IRAF environment you know a number of ways to display and manipulate images. The following section supposes a familiarity with IRAF, and is intended primarily as a suggested approach to begin evaluating data and testing images from the spectrograph. The spectra imaged by the spectrograph may not be perfectly aligned along columns, and the transmission optics of the spectrograph introduce some geometric distortions. Thus a more sophisticated approach is generally needed to view a spectrum than simply plotting columns or rows, and better sky subtraction is possible when these geometric problems are accounted for. The IRAF apall package is designed to do this preliminary geometric calculation, spectral extraction, and sky subtraction. The following is a cookbook to get started with apall, but you are strongly urged to read the help manual for apall to branch out from the technique outlined below. 8.2. Setup Once in the IRAF environment, you must load the spectrographic IRAF processing packages; enter the following that are needed: cl> onedspec, on> twodspec, and tw> apextract. If spectra lie along CCD rows, enter: ap> dispaxis=1. If along columns: 172 ap> dispaxis=2. Next, set the processing parameters for apall. Apall is a program that converts your twodimensional image into a one-dimensional, extracted spectrum that is also sky subtracted. It does this by coadding pixels optimally across the dispersion direction (along the slit) of your spectrum at each pixel position along the dispersion, and then subtracting evaluations of the adjacent sky along the dispersion. If there are doubts that the previous user may have left the apall parameters set in disarray, enter: ap> unlearn apall Then, enter: ap> epar apall and, with the or arrows, examine the parameters and reset the ones mentioned below. Any that are not mentioned may be left as is. To change a parameter, move to it with the or arrow, type in the new value, then move on. You do not need to type a with each new entered value. The editting process is terminated with a control-. Parameters to set or modify: First group: format: multispec interactive: yes find: yes recenter: yes edit: yes trace: yes fittrace: yes extract: yes review: yes extras: no Default aperture parameters: lower: -2.5 upper: 2.5 Default background parameters: b funct: chebyshev b order: 1 b sample: -8:-4, 4:8 b nave: 1 b niter: 3 Automatic finding and ordering parameters: nfind: 1 minsep: 25 173 Tracing parameters: t nsum: 25 t step: 25 t nlost: 3 t niter: 1 Extraction parameters: background: fit skybox: 1 weights: variance pfit: fit2d clean: yes readnoise: 15 gain: * *To be determined. 8.3. Usage You must convert your FITS format frames to IRAF format. By way of example, a FITS frame called ccd117.fits would be converted as follows: cl> rfits ccd117.fits then answer IRAF filename: ccd117.imh to the “IRAF filename:” output file query. Unlike with most IRAF tasks, the extensions .fits and .imh should be typed in full. The use of apall described here is in interactive mode. This is recommended for getting your feet wet with the process. There are many layers of complexity you can add to this simple cookbook reduction with increased knowledge of apall. For example, cosmic rays in longer exposures of faint objects may occasionally require deviations from the process described. In this case, however, it is generally best to take multiple exposures (at least three) and attempt cosmic ray cleaning by stacking the images with the IRAF combine task, after setting the combine option to “median” and the reject option to “avsigclip”, for example. Two processes are here described: one for bright objects where a continuum spectrum is obvious across the entire spectrum, and one for faint objects where the continuum is faint or nonexistent. For Bright Objects: After converting to IRAF format, start the reduction of a frame with the example name ccd117.imh as follows: ap> apall ccd117.imh 174 Answer the first three questions asked with the default response (yes), which can be entered simply with a . The first graph shown in your gterm window is a section cutting across the spectrum along the slit. The finding algorithm will indicate what it thinks is the location of your object spectrum. If you had centered the object in the slit, then the spectrum should be in the center of the image. If the automatic selection looks right, typing a will accept it and move to the next step of processing. Occasionally the selection will not be correct, as in the case of a very bright cosmic ray contamination, or in the case of a brighter source somewhere else in the slit, or in the case that the comparison source was selected. If you wish to alter the selection of object spectrum, strike a to “delete” the automatic selection, place the cursor on the correct feature, and then strike to select a “new” choice; then hit to move to the next step. Respond with acceptance of default “yes” answers until the next graph comes up. If you wish to abort the procedure at any time, begin entering “no” responses to queries until you exit the program. The second graph shows the location on the chip where the spectrum was traced at each point along the dispersion. It corresponds to the centroid of the cross-section of the spectrum along the slit at closely spaced intervals along the dispersion. Not infrequently, a hot pixel or cosmic ray will introduce unacceptable deviations. When this happens, the program may automatically delete points in the interactive fitting procedure, or you can delete the points by hand by placing the cursor on the point and typing . Refit the spectrum by typing . You may want to improve the fit to the trace by changing the order of the fitting function (to, say, third order), by typing: :order 3 or by changing the fitting function to a Legendre polynomial or a spline3, :function spline3 Always refit the spectrum with a after any such alterations. You may finish the fit by typing . Apall will then ask if this fit information should be added to the database, to which a response will give the default (yes) response. Next, you will be asked to review the spectrum (yes), and to show the spectrum (yes). If all is well, a graph showing your spectrum will appear. However, if the spectrum was too faint, the program may bomb here with a variety of error messages, and you may have to use the other method for extraction described below. The graph displayed is the raw spectrum. If the object is faint, or the exposure is long enough to accumulate cosmic rays that dominate the graph scaling, the ordinate may be set so that your object spectrum is unusably compressed. You may redo the display by placing the horizontal cursor just above your spectrum and typing a “>” symbol, and then below your spectrum and typing a “<” symbol. Alternatively, you may quit the plot with a and redisplay using the splot task. When you quit, a response to the query about whether to write the plot to the disk. The program will ask you the name of the file into which to write out the extracted spectrum. It will pick a name it likes, but this name may be too long for your liking (the IRAF default is designed to accommodate multiple spectral extractions from one image), and you may wish to type a new name. Whatever you type will be appended with the suffix “.ms.imh”. For example, 175 if your image name is “ccd117.imh”, you may type in that you want the extracted, onedimensional spectrum to be named “ccd117”, and the raw, 1-D spectrum will ultimately be put into an IRAF format file called “ccd117.ms.imh”. You may then examine your spectrum with the IRAF program splot, by typing ap> splot ccd117.ms The splot package allows a very broad variety of manipulations that the user should peruse typing ap> help splot For example, you may set the x and y windowing of the plot with “:/xw” and “:/yw” commands. A very useful feature is boxcar smoothing excessive noise in your spectrum by typing and entering the smoothing width in pixels (3 or 5 are good values) followed by a . For Faint Objects: The procedure for faint objects is almost the same as given above for bright ones, with the exception of two parameter changes. An object that has a very faint continuum can no longer be extracted properly, since the centroid of the spectrum may no longer be traceable. In this case, you must have another exposure of a bright source in the same slit position as a reference. You need to turn off the automatic ”fittrace” routine and tell the program to refer to the other image. You can do this with the invocation of the apall routine as follows: ap> apall ccd117 refer=ccd116 -fittrace where in this example the reference spectrum is contained in the image ccd116.imh, which has already been reduced into ccd116.ms.imh beforehand. The minus sign before the “fittrace” turns off that option. Note: because of the effects of atmospheric dispersion, there may be differential shifts of wavelengths along the slit (see Fillipenko, 1982, PASP, 94, 715 for a description of the effects of atmospheric dispersion on spectrophotometry and how properly to minimize this problem with slit position), especially in the blue. In order to minimize the differences between reference spectrum curvature and target spectrum curvature, it is best to take both spectra at comparable sky position (airmass and hour angle) and the same slit orientation and positioning. 8.4. Extracting the Comparison Spectrum In order to do the wavelength calibration, you need also to extract your comparison spectrum. Hopefully your chip was well aligned along columns or rows, so that there is not significant rotation which will cause shifts in rows/columns between the comparison and target spectra. If this is the case, you will need to extract BOTH comparison sources, do individual wavelength calibrations for each, and then interpolate the wavelength shifts as a function of distance between them. 176 Extracting the comparison source spectra is done similarly to the target object spectra above, with a few exceptions. First, you need to store the extracted spectrum in a place other than the apall default name, by explicitly specifying a name. Second, because the comparison sources are quite extended, you want to ensure that the “background subtraction” region picked is outside the area on the image occupied by the comparison spectrum. In the following example of an apall call, the b sample keyword is specified to account for: (1) the image is 2x2 binned, (2) we are dealing with the right hand comparison spectrum in Figure 4, and (3) the background sampling region is made further away from the center of the comparison source to be in a “blank” part of the image: apall bs8520b2 b sample=”-35:-25,40:50” output=bs8520b2.comp The output image name will be bs8520b2.comp.ms.imh. When the first graph is displayed by apall, ensure that you are on the correct place for the comparison spectrum you want (compare the imtool position for example). If not, move the extraction to the correct place. The graph showing the trace will show a lot of scatter, but this is a function of the few well exposed places of spectrum (i.e., where the lines are) it has to work with. Therefore, it is recommended that a low-order fit, say linear, be used for the trace. 8.5. Wavelength Calibration For wavelength calibration of your spectrum, use the IRAF identify command. Before doing so, you need access to a data file containing a list of line identifications for the comparison sources you used (Hg, Ne, or Hg+Ne). In Appendix A, an atlas of these sources, as well as a line list for IRAF is given. You should ask your TA for the location of this linelist file so you do not need to type it in. Invoke the identify command on your image, specifying the linelist file (in the example here, which has both Ne and Hg, the linelist is given the name idhehg.dat) specifically: identify bs8520b2.comp coordlist=idhehg.dat You will then be presented with a graph of the extracted spectrum, as in Figure 6a. Pick a line that you think you recognize, place the cursor over it, and type an “m”. The program will ask you for the wavelength of the line and it’s name, which you should take from the linelist. In the example, the feature at pixel 363 is the 4358.35 ˚ Aline of Hg, and you would reply to the query 4358.35 Hg Do this again for at least one, but hopefully two other widely placed lines that you recognize. For example, the feature at pixel 154 is 5460.753 Hg(I) and the feature at pixel 80 is 177 5852.4878 NeI(6). At this point, the program will attempt to fit all of the other lines that it can. Type an “l” to match other features with lines in your linelist. As soon as you do, you will be presented with a graph where the features are now shown in wavelength space, as in Figure 6b. Note that the little dashes show the locations of expected features in your linelist; they should match the features in your spectrum. Typing a “?” at any time will result in the presentation of a list of options for reworking the wavelength calibration. For example, use the “+” and “-” keys to step through the line identifications. If you screwed up your identifications, you can type an “i” to initialize. Typing an “f” will give rise to a graph as in Figure 6c, which shows how well the current fit of the dispersion works for your linelist. In general, the RMS residual should be less than 1 and you should have no residual in the pixel to wavelength mapping more than a few pixels. You seen in FIgure 6c that the fit is worse in the blue. This is because there are fewer blue lines in this comparison spectrum to constrain the fit. You also see that a first order spline3 function was used to to the fit. If you would like the fit to remove certain points, either remove the points you don’t like with the cursor and the “d” key, or type :niter 10 to have the program iteratively throw out n-σ outliers, where the n is given by the low rej and high rej options. Make sure to type an “f” after each change in parameters. Use the h, i , j, k, and l keys to look at various representations of your fit. For example, “h” gives the actual fit, instead of the residuals (Figure 6d), “i” gives you the fitting errors in terms of Doppler velocity shifts (Figure 6e), whereas “l” shows the non-linear component of the fit (which in the example of Figure 6e we can see there is some curvature in the dispersion solution). Type a “q” to leave the fitting window. Type another “q” to leave the program and create a database file with your solution. In the case here, the database file is database/idbs8520b2.comp and it contains the list of matched lines and the fitting parameters selected. This database will be needed to correct your target spectrum. 178 Figure 6. Doing the wavelength calibration in IRAF. 179 180 Chapter 15 The Astrovid 2000 Video Camera 181 182 Astrovid 2000 Video Camera (Rev. August 06, 2007) 1. General Information The Astrovid 2000 CCD video camera was purchased in early 1999 from Adirondack Video Astronomy (www.astrovid.com). Its primary intended purpose is as the detector for the speckle interferometry system, but its light weight and simple controls also make it ideal for establishing a quick and direct video feed from the telescope. Note, however, that the video camera should not be thought of as an integrating device since the maximum exposure time is 1/60th of a second. The Astrovid is best applied to the viewing of bright objects (the moon, planets, bright stars) in real time, and the recording of high frequency phenomena (like speckles and seeing motion). An integrating CCD like the SBIG ST-8 is better for faint objects. The Astrovid camera is designed for use with a standard 1.25” eyepiece mount. An adapter has been constructed for the McCormick 26-inch refractor on the side of the flipmirror system at the end of the tailpiece. A small portion of the total eyepiece field of view can be imaged with the Astrovid camera by moving the tailpiece flip mirror to its secondary position. The video output can either be directed to the high-resolution monitor soon to be located in the dome room or directly into the McCormick laptop PC for the purpose of frame-grabbing. The following manual explains how to set up the camera, use its controls to obtain an optimal image, direct it’s video feed to the desired output device, and capture digital images in TIFF format for later analysis. General information about the camera and detector are summarized below. Note that the CCD in the Astrovid 2000 camera does not have square pixels. Astrovid 2000 CCD Sony HAD ICX038DLA Chip Size 7.95 mm × 6.45 mm Pixels 811 (horiz) × 508 (vert) Pixel Size 8.4 µm (horiz) × 9.8 µm (vert) Power Supply 12 V DC Weight 300 g Operating Temp 20 C to 55 C 183 2. 2.1. Setting Up the Camera Mounting the Camera The Astrovid 2000 CCD camera should have been mounted by the TA or the Observatory staff in preparation for your lab. If it is not, use care in following these directions. On the side of the McCormick 26” tailpiece, there is a mount with a threaded nut that accepts a roughly 1-5/8” diameter threaded cylinder. This was designed to accept the SBIG ST-8 CCD camera. The speckle system and Astrovid 2000 mount have been designed to fit this mounting point as well. The 1.25” mount for the Astrovid is a 2”-long brass cylinder with threading at one end and a slit cut lengthwise through the other. This slit allows the camera barrel to be locked into place with the aid of an aluminum ring clamp that fits around the mounting barrel. There is an aluminum protector ring that fits over the threading when the mount is not is use; this acts to keep the threads from becoming damaged. To mount the camera to the tailpiece, first remove the thread protector ring from the brass cylindrical mount. Next, align the threading with the mount extending from the tailpiece and lock it in place with the threaded nut. Slide the camera barrel in and tighten the aluminum ring clamp firmly about the barrel mount. This is accomplished by sliding the ring as far toward the camera as is possible and tightening the thumb screw; the thumb screw should be aligned roughly 90◦ from either lengthwise cut in the mount. Make sure that the camera is oriented so that it is perpendicular to the underside of the tailpiece. Refer to Figure 1. Note that the support brace seen in the images is not used with the video camera. Figure 1. Camera mounting on the 26-inch tailpiece. Left: flip mirror system with open mount. Right: Astrovid camera mounted to flip mirror system 184 2.2. Connecting the control box and power supply The control box has a roughly 6-foot cable that acts as a communication line to the camera itself. The box can be temporarily attached to the back end of the telescope during operation. Once the camera is in place, the two connectors at the end of this communication/video cable should be inserted into the appropriate jacks in the back of the camera. There is a BNC connector (refer to Figure 2 on the control box to which a coaxial cable can be attached. This is the video output, which can be directed to a monitor or computer. Once all of the above steps are complete, the power line may be attached. At the present time, there are no free outlets on the power strip attached to the 26-inch telescope. There is, however, a white 12-Volt adapter attached which is not necessary for the use of the Astrovid camera. This can be unplugged and temporarily belayed. Since there are several free-hanging cables and the extra power supply is somewhat heavy, one should be careful to avoid getting hit by freely swinging objects. The black 12-Volt adapter that comes with the camera should be plugged in to the now-empty spot on the power strip and the other end connected to the control box. A red light on the camera itself will now be illuminated. At the time this manual is being written, the camera control box and power supply are not attached to the telescope and must be connected and removed each time the system is set up. In the near future, however, a very long communication/video cable will be run from the tailpiece up the telescope tube to the axes of rotation, and then down to the main telescope control panel. The control box and power connector will be located on the pier for easier use. When this layout is implemented, setting up the video system will simply involve attaching the camera to the tailpiece, connecting the free-hanging cables, and turning on a display device. Figure 2. 2.3. Cable connectors from left to right: RCA, BNC, F Adjusting the Focus Once the camera is in place, the tailpiece position must be adjusted to move the CCD into the focal plane of the objective. Using the crank found on the pier, rotate the tailpiece adjustment bolt until the tailpiece position indicator is aligned with the marker labeled “speckle camera”. See Figure 3. This will bring the camera into rough focus. More refined focusing with the video camera is relatively easy because of the fast readout. The ideal focus may be checked by frame-grabbing images of unsaturated stars and checking the point spread function (e.g., with the MIRA software). 185 Figure 3. 3. Adjusting the tailpiece for proper focus Setting Up a Video Output Device There are two possible video output devices: a TV monitor and/or PC. At the current time, the only monitor available is a large television that is kept in the observer’s room and must be carried into the dome room. In the near future, a high resolution monitor will be acquired and most likely mounted on the pier in the dome room; this will make set-up very simple. To use the television as an output device, one simply needs to attach the f-type connector on the coaxial cable to the “ANTENNA” port of the TV. To use the McCormick laptop PC as a display device, first make sure that the “Videoport Professional” PC card is inserted into one of the two PC slots on the side of the computer. There is a connector that plugs directly into this and at the other end accepts an RCA plug. An RCA-to-F-type male connection adapter should be attached to the RCA connector. To this adapter should be attached a small female-to-female F-type connection adapter. The coaxial cable from the camera control box can be attached to this. Use of the frame-grabbing software for viewing and capturing the video output is discussed in a subsequent section. When the new high resolution monitor and long communication cable are in place in the dome room, the monitor will be set up semi-permanently to receive video feed in the following manner. The control box will live on the pier and the coaxial video feed will be attached to a “T” splitter which will also be attached to the pier. One of the two outputs from this splitter will be attached to the monitor so that all one needs to do to view the camera output is attach the camera to the tailpiece, turn on the power, and turn on the monitor. The other output from the splitter will have a free cable which can be attached to the PC card in the laptop if desired. In this way, the monitor can be used for easy viewing while the laptop can be used for frame grabbing. 186 4. Camera Controls The Astrovid 2000 system consists of a control box, power adapter, video cabling, and the camera itself. In this section we will concentrate on the control box. There are 3 controls that can be adjusted to help produce an optimal image. 1. The Shutter Speed controls the length of each individual video frame exposure. There are 2 OFF positions and 8 ON positions with differing shutter speed. The longest shutter speed is 1/60 sec; note that this is not long enough to allow direct video imaging of low surface brightness objects. 2. The Gain controls the amount of signal amplification. The gain is off when the indicator points to the left and is at its maximum when pointing to the right. 3. The Gamma control adjusts the contrast in the image. By using various combinations of SW 1 and SW 2 in their 2 positions, varying contrast levels can be chosen. The goal is to adjust the various controls in such a way as to produce an image with the best signal-to-noise, contrast, and dynamic range for your application. Increasing the gain results in an amplification of the signal in all pixels: in addition to amplifying the pixels of interest, the overall noise in the image is also amplified. When possible, it is preferable to produce a brighter image by decreasing the shutter speed rather than increasing the gain. The result will be a cleaner image. The following is a summary of the various possible control settings: Shutter Switch Setting Time (sec) 0 1/10,000 1 1/4,000 2 1/2,000 3 1/1,000 4 1/500 5 1/250 6 1/125 7 1/60 8 off 9 off 5. Gain control Clockwise Decrease gain Counter clockwise Increase gain SW SW SW SW SW SW Gamma Setting Gamma = 1.0 1 Up Normal Mode 2 Don’t care 1 Down Gamma = 0.45 Medium Contrast 2 Up 1 Down Gamma = 0.2 High Contrast 2 Down Centering the Image on the CCD Getting the desired object centered in the video camera CCD can unfortunately be a bit challenging. Since the chip is small, it sees only a small fraction of the total field visible in 187 the eyepiece. The CCD field of view is, however, fairly well centered in the eyepiece field of view. To get the object of interest to appear on the display device, first find it by eye using the eyepiece. Get it centered as much as possible in the field of view. Now move the flip mirror on the tailpiece to redirect the light into the camera. If the object does not appear on the monitor, try adjusting the gain and exposure time. If it still does not appear, you may have to make some small adjustments to the pointing of the telescope to move that section of the image onto the chip. 6. Capturing Images With the McCormick Laptop PC To capture digital images from the Astrovid 2000, first connect the coaxial cable to the sequence of adapters that lead to the PC card in the laptop computer. Run the program called “Image Wizard”. From the “File” menu, select “Scan...”. Alternatively, there is a shortcut button in the lower left corner of the control panel that issues the same command. Select “Acquire” from the box that pops up. You should now see a window which looks something like that shown in Figure 4. Make sure that “Greyscale” is selected in the “Picture” box and that “1/1” is selected in the “Size” box. You should see the live video output from the camera in the preview box. Note that the capture rate through the PC vie “Acquire” is not as fast as the live video rate seen through the monitor (i.e. the PC does not show every integration frame). When you’re ready to capture an image, click on the “Capture” button and then on “Ok”. The image you’ve just captured should appear in the main window of the program. Repeat this process to capture further images. Figure 4. Image Wizard TWAIN acquire window Be conscious of the number of open windows on the desktop. Capturing too many images without saving may result in memory problems. Desirable images should be saved to disk 188 periodically and their windows should be closed unless they are needed for reference. Images should be saved in TIFF format. Most image analysis and manipulation programs can read TIFF images. Also be conscious of the amount of available hard drive space on the laptop. Data should be saved on the laptop only temporarily. It is preferable to transfer image data to another disk when possible. You may want to capture and co-add a series of images. Note that the rate of image capture is dependent on the bus transfer rate and processor speed of the computer, but each captured frame is of the integration length selected on the control box. To co-add a series of captured images, select “Averaged Capture...” from the “Video Capture” line in the “File” menu. See Figure 5. You should see a window similar to that in Figure 6. You can specify the number of frames to be captured as well as the division factor. If you want to simply accumulate frames without averaging, you would leave the “Divide Result by: ” box set to one. For complete averaging, both boxes should contain the same number. Figure 5. Image Wizard File menu and Video Capture selections Figure 6. Image Wizard video averaging 189 7. Shutting Down Please leave the Astrovid 2000 and the telescope as you found them. If the camera was installed when you arrived at the telescope, then leave is installed. At the end of the night, be sure to shut off the TV monitor and/or laptop. Disconnect the power to the video camera, but leave it attached to the tailpiece. Either a TA or the Observatory staff will remove it when necessary. If you installed the Astrovid camera system, please uninstall and store the camera in the equipment cabinet where you find it. Finally, re-stow the telescope in the standard way. 190 Chapter 16 The Astronomy Library and Astronomical Literature 191 192 The Astronomy Library and Astronomical Literature (Rev. August 09, 2011) 1. The Astronomy Library The Astronomy Library is one of the departmental libraries associated with the Science and Engineering Library. It is located in the Astronomy Building in Room 264. It is accessible via key access only. The Astronomy Library holds material supporting graduate academic programs as well as advanced research in astronomy and mathematics. It contains more than 13,000 books and 265 journal and serials subscriptions. Astronomy and Mathematics materials are shelved as separate collections. Unbound journal issues are shelved alphabetically by title. Bound journal volumes are shelved by call number. The Astronomy Library houses the specialized Astronomy books, conference proceedings, observatory reports, periodicals (journals) and reference books. Ph.D., M.A., and undergraduate Senior theses generated by the Astronomy Department are also displayed in the library. Some general astronomy books are kept in the larger Science & Engineering Library in Clark Hall, and some older journals and books are now stored in the Ivy Stacks where the air quality is well controlled. The most recent volumes of periodicals are kept on a special shelf in the library near the librarian’s desk. Reserve books are located on a shelf behind the librarian’s desk. The most recent book arrivals are displayed on the bookshelf next to the new periodicals. Do not re-shelve any materials which you use in the library. Please leave them on the counter in front of the librarian’s desk. No food or drink are allowed in the Astronomy Library!∗ Food attracts pests which then feed on the paper in the library’s volumes. Failure to comply with this restriction will result in loss of library privileges. ∗ For more information on the Astronomy Library, check the World Wide Web at http://www.lib.virginia.edu/science/scilibs/astr-lib.html and for more details select Collections from the first web page. 1.1. Reference and Information Services The Astronomy Library provides instruction in the use of both electronic and traditional reference tools, in addition to helping you with specific reference questions. You may contact 193 Beth Blanton-Kent for personal assistance: (e-mail: [email protected]), call 924-6837, or chat on IM to selblanton. 2. Guide to Astronomical Literature For astronomers, professional and amateur alike, information is obtained from a variety of sources. Here is a brief introduction to these sources, their use and utility. A list of these sources would include journals, texts, books, catalogs, atlases, almanacs, conference proceedings, observatory reports, emphermides, charts, magazines, databases, etc. The following is a general description of each type of reference, its particular use and lists of the more prominent examples. You will see that astronomers utilize a diverse set of references both to carry out investigations and to keep abreast of current research. A thorough understanding of their use is essential to productive work. 2.1. General Guides Two old but very good guides to astronomical literature are: Seal, Robert A. 1977, A Guide to the Literature of Astronomy, Littleton, Colo., Libraries Unlimited. (Z 5151.S4) Kemp, D. A. 1970, Astronomy and Astrophysics; A Bibliographic Guide, London, MacDonald Technical and Scientific; distr. Hamden, Conn., Archon Books, Shoestring Press, Inc. (Z 5151.K45) The first book in particular contains helpful information for finding your way around an Astronomy Library. Be forewarned: Books dealing with astronomy are assigned Library of Congress numbers by librarians not astronomers. 2.2. The Age of the Computer The advent of the World Wide Web (WWW) has enabled access to many online electronic computer databases. Most libraries now have computerized lists of their holdings (e.g., the UVa Libraries) and provide access to other libraries. Books can even be requested and reserved electronically. Literature searches can now be effectively accomplished sometimes purely by computer. Some journals, like the Astrophysical Journal Letters, are now accepting manuscripts and displaying refereed papers electronically in addition to the usual paper copy. However, it will be a while before we have no need for the reliable hardcopy of our favorite journals. For lists of astronomical databases you can begin with the following WWW addresses: http://www.astro.virginia.edu/www/ or http://www.lib.virginia.edu/science/scilibs/astr-lib.html 194 2.3. Periodicals/Journals Journals are periodical (weekly to yearly) softback publications designed to give the reader up-to-date knowledge of the astronomical world. One can loosely subdivide journals into three categories: professional journals, popular astronomy magazines, and general science journals. Professional journals contain technical research reports. This is where an astronomer learns of current advances in all fields of astronomy and where a researcher presents his/her work to the scientific community. Articles published in professional journals normally follow strict editing guidelines, are abstracted and heavily references, and have been refereed before publication. General science journals also contain research reports, but cover many scientific fields. Popular astronomy magazines attempt to bring a larger audience the excitement of current astronomy and space research and explain to the educated layman the sometimes exotic objects and processes which populate the universe. Also, popular astronomy magazines present sky charts, updates on visible planets, eclipses, comets, etc., articles of interest to amateur telescope makers, and serve as an advertizing medium for astronomy related items. Following is a list of the more important journals. Astrophysical Journal (ApJ) - University of Chicago Press This is the premier professional journal. Published twice monthly it contains research articles on all subfields of astronomy Articles containing large amounts of data are published in the Astrophysical Journal Supplement Series about five times yearly. Astronomical Journal (AJ) - American Institute of Physics Equal in stature to the Astrophysical Journal, the Astronomical Journal is published monthly and contains fewer articles. Content is similar to ApJ. Monthly Notices of the Royal Astronomical Society (MNRAS) The primary British professional journal, and the oldest continuous astronomical publication. Format and style is similar to ApJ. Astronomy and Astrophysics (AAp) - Springer-Verlag This is the primary European research journal and contains articles on all subfields of astronomy by primarily European astronomers. It also has a supplement series. Science - AAAS A weekly journal containing articles in all scientific disciplines, but emphasizing biology. This journal also published articles and editorials concerning science policy which are of interest to the astronomer. Nature - MacMillan Journals Very similar to Science, published in Great Britain. Weekly. Science News A weekly science newsletter geared toward the scientist and science oriented layman; it is not a research journal. Major scientific discoveries and results of space missions reach here long before they appear in professional journals. Science News is the “Time Magazine” of the scientific world. 195 Sky and Telescope - Sky Publishing Company Sky and Telescope has no peer as a popular astronomy magazine and is read by most professional astronomers as well. No other periodical appeals to so broad a range of interests in astronomy. Astronomy A recent (compared to Sky and Telescope) popular astronomy magazine published monthly, Astronomy is designed more for the amateur. Feature articles tend to have a ’gee whiz’ style; there are many colorful illustrations. The Astronomy News section is especially useful. There are dozens of additional professional journals (the astronomy department receives about 25 different journals). Because the time between completion of a paper and publication in a journal can be longer than a year, astronomers rely increasingly on preprints which are sent out when a paper is completed (before or after refereeing). Distribution of preprints occurs informally among researchers and astronomy libraries. 2.4. Conference Proceedings Astronomers frequently attend symposia, conferences, meetings, etc., and deliver research papers. The collected papers of such a meeting are a very important source of information. Their importance lies in the fact that most subfields of astronomy have no text which gives up-to-date knowledge of that subfield. A conference organized on a particular topic provides an excellent summarization. Some of the most significant conference proceedings are the IAU symposia and colloquia (blue, cloth covered volumes). 2.5. Observatory Reports All major and many minor observatories and astronomical research institutes publish research reports describing the activities at that institution. Frequently they are entitled “Publications of so-and-so Observatory”. In the early days of astronomical research (prior to WWII) observatory publications were the primary method of disseminating research results. They have subsequently been supplanted by the professional journals. Today the publications of many major observatories contain fewer research reports, and deal with staff, instrument upgrades, and computer programs. There are two publications of particular utility: Bulletin of the American Astronomical Society (BAAS) This publication, available to members of the AAS, contains observatory reports which describe the ongoing research programs of that observatory. Published on an annual basis. IAU Circulars Distributed by the Central Bureau for Astronomical Telegrams, located at the Harvard-Smithsonian Astrophysical Observatory, these cards are designed to call attention to recently discovered and/or transient phenomena so that world observatories can quickly place them under observation. Frequent items are: variable star outbursts, new comets, supernovae in external galaxies, and enhanced activity in active galaxies (QSO’s). 196 2.6. Review Literature In addition to conference proceedings, review articles are the other major source of information which summarizes a topic or subfield of astronomy. Below is a short list of review literature. Frequently an “invited lecture” to a conference will be a review and is printed as the first paper in the conference proceedings. Occasional monographs by senior astronomer provide excellent reviews. Annual Review of Astronomy and Astrophysics Published since 1963, this journal contains about 15 essays on various topics selected by an editorial board of leading astronomers. Essentially non- mathematical technical articles of about 30 pages in length. Extensive references given with each article are very useful to the student. Comments on Astrophysics This small publication, published about 3 timers per year, contains technical (and mathematical) reviews, normally 3 papers to an issue. Scientific American The major popular science review magazine, it is published monthly invariably with at least one astronomy related article. It is geared for the scientist and very educated layman; contains about 8 twenty page papers illustrated with colorful diagrams and photos, often written by an eminent astronomer. 2.7. Abstracts There is one major index to astronomical literature; Astronomy and Astrophysics Abstracts published semi-annually. It contains the abstracts of all articles published in the major journals, exactly as those abstracts appear in the journal. Entries are divided into 108 separate categories by subfield. In addition to research and review articles, conference proceedings, books, texts, atlases, etc. published during the 6 month period covered by the volume are listed. There are two indexes; by author and subject (not by title). The subject index is good but not comprehensive. Since these abstracts are always about a year behind, an offshoot has appeared since 1976, “Astronomy and Astrophysics Monthly Index”. This contains an author and title index but no subject index. 2.8. Almanacs, Data Books, Handbooks This category of the literature can loosely be defined as sources of data which the astronomer needs to successfully complete observations. The Nautical Almanac An indispensable text for every observatory; the Nautical Almanac is published yearly by the U.S. Naval Observatory. It contains voluminous information on mundane, daily, astronomical phenomena like sunrise, sunset, moonrise, positions of the planets and their satellites as well 197 as formulae for calculating the positions of celestial objects. Tables give current epoch positions of bright stars, galaxies, and radio sources. Astrophysical Quantities by Allen This text represents the current (publication date) state of knowledge about celestial objects. Divided into many categories, it gives such data as the masses, sizes, distances, and orbital periods of the planets, lists of the brightest and nearest stars, temperature and luminosities of various stellar types and so on. The quickest way to find a particular value in astronomy is pick up this book. The last edition was published in 1973 and is becoming outdated. Astrophysical Formulae by Lang This text contains hundreds of astronomical and physics formulae and complements Allen’s work. Astrophysical Data (1991) by Lang The latest most up-to-date listing of astrophysical data. In two volumes. 2.9. Charts and Atlases Reference works in this category are an essential tool for observational astronomy for amateurs and professionals alike. An astronomical atlas is a representation of the sky or some object in the sky (esp. the moon) and consists of either photographs, maps or overlays. Many atlases are “all sky” maps (e.g., Palomar Observatory Sky Survey, SAO atlas), some map out a particular type of object (AAVSO Variable Star Atlas), others present a compilation of objects (Hubble Atlas of Galaxies, MK Atlas). All of these works aid astronomers in preparing and subsequently reducing observations. The advent of the space age has opened up new areas of the spectrum for observation; here atlases help identify objects found to be emitting in the ultraviolet, infrared, etc. Some major works are: Smithsonian Astrophysical Observatory Atlas (and Catalog) This reference contains 152 charts covering the entire sky on which stars to about 10th magnitude and many non-stellar objects are plotted. Designed to be used in conjunction with the SAO Star Catalog (described in the next section). AAVSO Atlas Similar to the SAO atlas, variable stars brighter than 9.5 mag. (visual), and amplitudes greater than 0.5 mag. are plotted using 1950.0 epoch at 4’/mm. Norton’s 2000.0 Star Atlas Perhaps the most popular star atlas for amateur astronomers. Formerly Norton’s Star Atlas. The MK Atlas A photographic atlas depicting the standard stellar spectral classification system. Uranometria 2000.0 A photographic atlas of the Northern Hemisphere (Vol. I) and Southern Hemisphere (Vol. II), for stellar objects with magnitudes less than 9.5. 198 Palomar Observatory Sky Survey (POSS I): Photographic atlas of the Northern Hemisphere. European Southern Observatory (ESO): Photographic atlas of the Southern Hemisphere. New Palomar Observatory Sky Survey (POSS II): Photographic atlas of the Northern Hemisphere. SERC-EJ: Equatorial atlas The major sky surveys are listed in Table 2.8 of Mihalas and Binney’s Galactic Astronomy, and some major galaxy atlases are listed in Table 2.7 of that reference. 2.10. Catalogs As atlases are an astronomer’s right hand, catalogs are his/her left hand. Almost all work in astronomy prior to this century consisted of creating catalogs. The first astronomers cataloged the positions of stars, then later “brightness” (magnitudes). People like Herschel and Messier plotted non- stellar objects. Not until the final decades of the 19th century did physics oriented researchers begin investigating astronomical problems (classical mechanics excluded). Later, after the techniques of spectroscopy and photography were developed, it was possible to pursue the analysis of the properties of celestial objects. A list of some important Astronomical Catalogues is given in Table 2.6 of Galactic Astronomy. A useful recent stellar catalogue is the Sky Catalogue 2000.0 which lists the observed properties of stars down to magnitude 8.0. It is published in two volumes, and the second volume describes classes of objects, e.g., types of binaries. 2.11. Publisher’s Series There are two series of books which deserve special mention: Stars and Stellar Systems An eight volume set published by the University of Chicago Press which was designed to cover all aspects of astronomy. Now mostly out-of-date. Titles are: Telescopes (1960) Astronomical Techniques (1962) Basic Astronomical Data (1963) Galactic Structure (1965) Stellar Atmospheres (1960) Nebulae and Interstellar Matter (1968) Stellar Structure (1965) Galaxies and the Universe (1976) Astrophysics and Space Science Library Produced by D. Reidel Publishing Company, this series now contains over 80 volumes covering diverse topics in astronomy. Individual volumes have a variety of formats; many are conference proceedings. 199 2.12. Observational Astronomy Observational Astronomy undergraduate students. QB 145.B52 by D. Scott Birney (1991). Up-to-date. Intended for Modern Technology and its Influence on Astronomy edited by J. V. Wall and A. Boksenberg (1990). Selected articles on a variety of telescope designs from optical to radio. QB 84.5.M63 Data in Astronomy they are archived. QB 51.3.E43J37 by C. Jaschek (1989). Discussion of types of data and ways in which Observational Astrophysics by P. L´ena (1988). An up-to-date text. Intended for graduate students. Description of observing techniques, detectors, and data analysis procedures. QB 461.L46 Astronomical Techniques by C. R. Kitchin (1988). Good undergraduate text. Description of detectors and a variety of imaging techniques. Recommended reading. Q13461 Astronomy: Principles and Practice undergraduate level text. QB 43.2 by A. E. Roy and D. Clarke (1988). Good Astronomical Observations by G. Walker (1987). An up-to-date text. Intended for graduate students. QB 86.W35 Astronomical Techniques ed. by W. A. Hiltner (1962); Vol. II of Stars and Stellar Systems. An extensive text which gives a detailed description of optical observational astronomy (photometry, spectroscopy, photography, measurement and reduction of observations). It is one of the two basic texts in the field, but it was published almost 30 years ago and an updated version is needed. QB 86.H5 (Ast) Basic Astronomical Data ed. by K. A. Strand (1963); Vol. III of Stars and Stellar Systems. This volume gives the definition and calibration of the quantities which are used to characterize celestial objects. Recommended reading: Chapters 8, 9, 11, 12, 13. QB 801.S75 (Ast) The Astronomical Telescope by B. V. Barlow (1975). An excellent 200 page text. Recommended reading: Chapters 3, 4, and 7 (read during first week of semester). QB 88.B37 (Ast) Observation in Modern Astronomy by D. S. Evans (1968). A mostly descriptive text; it is an excellent supplement to Norton’s Atlas if you feel that the Atlas is too concise. 200 Recommended reading: Chapters 1, 2, and 3. QB 64.E86 (Ast) Tools of the Astronomer by G. R. Miczaika (1961). Mostly descriptive, but a bit out-ofdate. Recommended reading. QB 86.M5 (Ast) Methods of Experimental Physics Volume 12, Part A: Optical and Infrared, ed. by N. Carleton (1974). A comprehensive text. It is 600 pages in length and consists of a set of review articles on topics in observational techniques. Examples: Photomultipliers, Characteristics of Photographic Plates, Television Systems. Intended for graduate students. QB 465.A8 pt.A (Ast) 2.13. Data Analysis Practical Astronomy With Your Calculator by P. Duffett-Smith (1979). Topics include time, coordinate system transformations, orbits of planets, orbits of planets, eclipses, and spherical astronomy. QB 62.5.D83 Mathematical Astronomy With a Pocket Calculator by A. Jones (1978). Most of the programs described deal with spherical astronomy. This will be useful for computing current epoch coordinates, and reducing radial velocities to heliocentric values. QB 47.J66 (Ast) Data Analysis For Scientists and Engineers by S. Meyer (1975). A guide to scientific data collection, reduction, and analysis. Also contains extensive material on probability. QA 276.M437 Data Reduction and Error Analysis for the Physical Sciences by P. Bevington (1969). Discussion of errors, probability, curve-fitting, least squares, and simple statistical tests. QA 278.B48 2.14. Specific References Related to Observational Astronomy Telescopes The Astronomical Telescope by Barlow, especially Chapters 4, 5, 6. Tools of the Astronomer by Miczaika, Chapter 3, 4. Photometry Astronomical Photometry by Henden and Kaitchuck, the entire book Tools of the Astronomer by Miczaika, Chapter 5 Astronomical Techniques by Hiltner, Chapters 6, 7, 8, 9 201 Methods of Experimental Physics by Carleton, Chapters 1, 2, 9 Basic Astronomical Data by Strand, Chapters 9, 11, 13 Astronomical Papers Dedicated to Bengt Stromgren, a symposium held in May 1978. Mostly technical papers on the application of photometric observations. QB 1.A88 Introduction to Astronomical Photometry by Golay, Astrophysics and Space Science Library, Vol. 41 (1974). Graduate level text; not easy reading. QB 135.G64 Problems of Calibration of Multicolor Photometric Systems, Workshop proceedings held in May 1979. Pages 83 – 102 give a review of the DDO photometric system. Spectroscopy Tools of the Astronomer by Miczaika, Chapter 6 Basic Astronomical Data by Strand, Chapter 8 Methods of Experimental Physics by Carleton, Chapter 10 Astronomical Techniques by Hiltner, Chapters 2, 3, 4, 12 Spectral Classification “Fundamental Stellar Photometry for Standards of Spectral Type on the Revised System of Yerkes Spectral Atlas,” Ap. J, 117, 313 (1953), H. L. Johnson, W. W. Morgan. “Classification of Stellar Spectra,” Volume 3, in Stars and Stellar Systems: Basic Astronomical Data, 1963, Philip C. Keenan Henry Draper Catalogue, Harvard Annals, Volumes 91-99. “The Spectroscopic Absolute Magnitudes and Parallaxes of 4179 Stars,” Ap. J., 81, 187 (1935), W. S. Adams and A. H. Joy, M. L. Humanson, A. M. Brayton. An Atlas of Stellar Spectra, Morgan, Keenan, Kellerman (1943). An Atlas of Low Dispersion Grating Stellar Spectra, Abt, Meinel, Morgan, Tapscott (1968). Atlas for Objective Prism Spectra Bonner Spectral Atlas I, W. C. Seitter (1969). An Atlas of Spectra of the Cooler Stars Types G, K, M. S, and C, P. C. Keenan, R. C. McNeil (1976). A Multiplet Table of Astrophysical Interest C. E. Moore, 1945, Revised Edition, Princeton Contributions No. 20. see also: Atomic Energy Levels, Vol. I, 1949; Vol. II, 1952; Vol. III, 1958; National Bureau of Standards, Circular 467. Lines of Chemical Elements in Astronomical Spectra P. W. Merrill, 1958, Carnegie Inst. of Washington Publ. 610. The Solar Spectrum 2035˚ A to 8770˚ A C. E. Moore, G. H. Minnaert, J. Houtgast, National Bureau of Standards Monograph 61. The Ultraviolet Spectra of A- and B-Stars, O. Struve 1939, Ap. J., 90, 699. 202 Revised MK Atlas for Stars Earlier than the Sun Abt, Morgan and Tapscott, 1977 (referenced in the 1976 ”Atlas of Spectra of the Cooler Stars”). Bonner Spectral Atlas Part 2. Revised MK System, P. C. Keenan and R. E. Pitts 1980, Ap. J. Suppl., 42, 541. Photography Miczaika, Chapter 2 Carleton, Chapter 5 Hiltner, Chapters 15, 16 Modern Techniques in Astronomical Photography, in the proceedings of an ESO workshop held in May 1978. AAS Photo-Bulletin, an irregular publication devoted to photographic procedures. The latest cumulative index is on reserve. Kodak publications on photographic plate characteristics and plate cutting. Optics Miczaika, Chapter 1 Barlow, Chapter 3 Fundamentals of Optics by Jenkins and White. QC 355.2.J46 Fundamentals of Physics by Halliday and Resnick, Chapters 35 to 39 Physics by Tipler, Chapters 25, 26, 27. Spherical Astronomy Spherical Astronomy by Smart (1949). The Nautical Almanac QB 145.S6 General Astrophysics Introduction to Astronomy and Astrophysics by Smith and Jacobs. QB 47.B47 Outline of Astronomy by Voigt, 2 volumes. Several sections of this text deal with techniques as well. QB 62.V6413 Advanced Techniques Instrumentation in Astronomy, Volumes I, II, III. QB 86.I58* Scientific Research with the Space Telescope (an IAU Symposium). QB 88.S35 Auxillary Instrumentation for Large Telescopes, ESO/CERN conference (1972). QB 86.E18 Radio Astronomy 203 The Invisible Universe by G.L. Verschuur (1974). QB 475.V47 Radio Astronomy by J.D. Kraus (1986), Cygnus-Quasar Books Galactic and Extragalactic radio Astronomy by G.L. Verschuur and K.I. Kellermann (1988), 2nd edition, Springer-Verlag An Introduction to Radio Astronomy by B. F. Burke and F. Graham-Smith (1997), Cambridge University Press 204 Appendix A Using IRAF on a UNIX Workstation 205 206 Using IRAF on a UNIX Workstation (Rev. August 06, 2007) 1. Starting IRAF Once you have logged in to one the Department of Astronomy’s UNIX workstations, you will be able to use the IRAF software package to reduce and analyze your CCD data. The computer account you are using should already be set up to run IRAF. If it is not, see the department’s computer guru, Howard Powell, or your TA for help. To begin using IRAF, do the following: 1. Type cd iraf to move to the iraf setup directory. 2. Type cl to begin IRAF (cl means command language). 3. In another window, type: ximtool &. This will start an image tool window. 4. (To exit IRAF, type logout, or lo for short.) Once you have started IRAF, the prompt in the IRAF window will always be two letters followed by a “>”. For example, the prompt will be cl> after start up. These letters change depending on which IRAF package was last loaded. Note that once an IRAF package is loaded, you may access tasks within that package even if other packages have been loaded afterwards. Note that it is not possible to give a thorough treatment of the IRAF package here, but only an introduction. To learn more about any particular task taskname, you may type help taskname at the IRAF prompt. To find out which tasks have been loaded at any particular time, you may type a “??” at the IRAF prompt. IRAF is a huge program with many tasks and add-on packages. Only a small subset of the entire IRAF behemoth is covered here. 2. FITS vs. IRAF format IRAF will, by default, convert all images into a standard format only compatible with IRAF. It will work with FITS images, although this does entail some risk as the FITS kernel is relatively new. All the commands described below are designed to work with FITS images. You simply replace ”.imh” and ”.pix” with ”.fits”. 207 By default, IRAF will convert your image from fits to IRAF when any operation is applied ot it. Suppose your images have names like “ccd117.fits”. Any operation will convert the image into the standar IRAF format “ccd117.imh” and “ccd117.pix”. In this context, “.imh” is the suffix specifying the IRAF file (meaning “image header”). At this point it is necessary to make brief mention of the IRAF file format. IRAF was developed at a time when disk space was hard to come by but CCD images had already become reasonably sized. It was common at this time for there to be a “large-sized” disk shared by all users in a networked environment. The philosophy of IRAF was a compromise between the fact that users would want to have their images arranged within their personal directory structure, and the problem that these disk areas were usually too small to handle the images. Thus, each IRAF image has two files: 1. A “.imh” image header file that is small and that contains header information about the image (dimensionality, array size, number of bytes per pixel, etc.), as well as a pointer to where the real pixel data is to be found, and 2. The “.pix” file which contains the meat of the image, the large file of pixel values. Unfortunately, in spite of the fact that disks are much larger now, the versions of IRAF prior to 2.11 are wed to this dual file format and it is important to be mindful of it. Two rules must always be followed when dealing with IRAF images: 1. All operations you do with IRAF tasks must act on the “.imh” images (IRAF keeps track of the real manipulations with .pix files), and 2. Never perform UNIX operations on IRAF images that will change the directory locations of the “.imh” and “.pix” files. In general, it is not a good idea to do any UNIX operations on IRAF files; however, most UNIX operations (e.g., mv, cp, rm) have IRAF counterparts (e.g., imrename, imcopy, imdelete) that act on the coupled IRAF files. Always use the IRAF tasks for operations on images. You may want to leave images in FITS format so that they can be operated on by other programs, such as IDL. To do this you need to type: cl> reset imtype="fits" cl> flpr cl> reset imextn=".fits" You can also add the reset commands to your login.cl program to have it be the default. 208 3. Common IRAF Tasks We now briefly turn to the most commonly used IRAF tasks that you will want to use. Again, read the help files of these tasks to learn the full capabilities. For each IRAF task, there are two sets of associated parameters: hidden parameters which, once set, remain held until changed explicitly, and unhidden parameters which must be set every time the task is invoked. The list of unhidden and hidden parameters for a task may be seen by typing cl> lpar taskname The hidden parameters are the ones shown in parentheses when you do an lpar command. Unhidden parameters may be typed on the command line, but if not included there, you will be asked for them by the program. For example, to display an IRAF image in your imtool window, use the display task: cl> display ccd117.imh Note, if you simply type cl> display you will then be asked image to be displayed (): Anything written in the parentheses after such a question is considered a default, and can be accepted with a simple . The default is generally related to the last time you successfully invoked the same command. For example, if you had previously display an image “ccd116.imh”, you would have been asked image to be displayed (ccd116.imh): Hidden parameters may be changed in several ways. At any point you may change a hidden parameter at the IRAF command line, as in the following example: cl> display.fill=yes In this example, the hidden parameter “fill” of task display is set to “yes” and will remain so until changed again. The display.fill option tells IRAF whether to squeeze down an image to fit it entirely into the full display region of ximtool if set to yes, or to display only the central portion of the image with a 1:1 mapping of pixels into the 512x512 ximtool display area. When many parameters need to be changed for a task, use the epar command, e.g.: cl> epar display which will then bring up the full menu of both hidden and unhidden parameters. Use the or arrows to examine the parameters. To change one, move to it with the or arrow, type in the new value, then move on. You do not need to type a 209 with each new entered value. When you are finished editting parameters, exit with a control-. Alternatively, you could have changed the hidden parameter at the invokation of the command display: cl> display ccd117.imh fill=yes but note that in this case the hidden parameter is changed only for this single invokation of the display command, and will revert back to the default fill=no when the command is finished, unless it had already been previously set to fill=yes. Here is a list of other IRAF tasks you may find useful (note: you need only type an IRAF command to the point that the typed letters specify a unique IRAF task): • imdelete - delete a “.imh” file and its associated “.pix” file • imcopy - make a copy of the image • inrename - rename an image, or move it to a new directory (specify as the new name the directory path and file name) • imarith - do mathematical operations between images of similar dimensions or between an image and a constant scalar value • imcombine - combine (average, median, mode) a set of images of the same dimension • imhead - give information about an image • implot - plot columns or rows of an image • imhistogram - plot a histogram of the pixel values in an image • imstatistics - calculate statistics of an image • minmax - tell the minimum and maximum values in an image • pcol, pcols - plot column or columns of an image • prow, prows - plot row or rows of an image • contour - make a contour plot of an image • surface - make a surface plot of an image • imexamine - a more sophisticated version of implot that interacts with the imtool display of the image and with many useful facilities, including those of implot, contour, surface, imstatistics, etc. 210 Finally, a word on image sections. Any of the above IRAF operation may be performed on image sections. In IRAF, the x-dimension of an image is specified as columns, and the ydimension is specified as rows (or lines), and described always in the specific order [columns, rows]. For example, if you do an imhead on an image, you will get back the dimensions of the image as, e.g., [2048, 2048]. But you may also operate on specific sections of images by specifying rows and columns explicitly, and with a “:” as the delimiter for ranges. For example, to display only columns 101 to 200 and rows 301 to 400 of image ccd117.imh, you would type cl> display ccd117.imh[101:200, 301:400] and to copy line 233 of image ccd117.imh into a separate image, ccd117.233.imh cl> imcopy ccd117.imh[*,233] ccd117.233.imh where here the “*” wildcard specifies all columns. In most operations of IRAF, the “.imh” is assumed, so that cl> imcopy ccd117[*,233] ccd117.233 would operate identically to the above command. 4. Image Reduction in IRAF This section of the IRAF manual is intended to provide students with a standard method for reducing CCD images. Please note that the manual is not exhaustive. For a thorough treatment of the subject, refer to Phil Massey’s A User’s Guide to CCD Reductions with IRAF on the NOAO web page or the printed version in Kerchoff 313. The images that you will obtain from the department CCD’s are not perfect. They contain various systematic effects which distort the images. The removal of these systematic effects, achieved by comparison with calibration images, is the process of reduction. This section will detail how to remove the overscan, trim an image, subtract the bias, subtract the dark current, divide by the flat field, and divide by the illumination. The result should be a nice clean flat image. The entire process of reduction hinges upon your having a set of “calibration images.” These images, itemized below, are what you will use to calibrate the object images—the picture that you want to process. Read this list before observing. Bias Frames: frames taken with a zero exposure time with the shutter closed. You should have 10 of these for each night that you observed. 211 Dark Frames: frames taken with the shutter closed. These monitor the induce thermal current of the chip. The ST-8 and smaller CCD’s will take darks automatically at your request. These are thermo-electrically cooled CCD’s and the dark current is substantial. You will need to actively take dark frames for each combination of temperature and exposure time. The Fan Mountain CCD is liquid nitrogen cooled and has negligible dark current. You should only need one long dark frame per observing run as a check on the dark current. Flat Fields: images of a uniformly illuminated screen (also called dome flats). You need to do at least 10 (preferably more) for each filter that you used (B,V,R, etc.). If you remove the CCD from the telescope or reposition it or the filters, you will need to take an entirely new set of flat fields. Sky Flats: also called illumination images or twilight flats. These are exposures of the twilight sky. Your data images can also be included in this set, providing you have a large number of frames with plenty of sky (i.e., your target objects are small). You should have about 10 illumination images in each filter. Again, if you remove the CCD from the telescope or reposition it, you will need to take an entirely new set of flat fields. 4.1. Procedural Overview A short description of the image reduction process follows. Overscan and Trim Correction: the overscan strip of the CCD is used to correct voltage drifts in the readout amplifier. Once corrected, the image is trimmed to revmoe the overscan region around the image as well as any bad edges. Bias Correction: the pixel-to-pixel DC voltage level inherent in the chip is subtracted. Flat Field Correction: the image is divided by a uniformly illuminated image to correct for pixel-to-pixel variation in quantum efficiency. Dark Correction: the dark current is subtracted from the image. Illumination Correction: the image is divided by a combination of sky images to correct for wavelength dependent low frequency errors in the dome flats. 4.2. The CCDRED Package To load the CCDRED package, start up IRAF (by typing cl), type imred to load the image reduction package then ccdred. The procedures you will use within the CCDRED package are: • ccdproc - the workhorse of CCDRED. This is the basic process that can be used to run all the important reduction tasks. 212 • imcombine - this process will combine multiple calibration images into a single image. • darkcombine - a variation of imcombine for dark frames - weighs dark frames by their exposure time. • ccdlist - will list images in the current directory, allowing the user to quickly determine what images he has and in what state of processing they are. • mkskycor - will combine sky images into a super-sky-flat and smooth it. • setinstrument - will allow the user to list the filters used in the data set. This is especially useful when used with ccdlist. It’s probably wise to start off with all CCDPROC’s options turned off. Edit the CCDPROC parameters (used eparam to start, :qw when done) until they read: images = (ccdtype= (maxcac= (noproc = (fixpix = (oversca= (trim = (zerocor= (darkcor= (flatcor= (illumco= (fringec= (readcor= (scancor= (readaxi= (fixfile= (biassec= (trimsec= (zero = (dark = (flat = (illum = (fringe = (minrepl= (scantyp= (nscan = (interac= (functio= (order = List of CCD images to correct ) 0) no) no) no) no) no) no) no) no) no) no) no) line) ) ) ) ) ) ) ) ) 1.) shortscan) 1) no) chebyshev) 5) CCD image type to correct Maximum image caching memory (in Mbytes) List processing steps only? Fix bad CCD lines and columns? Apply overscan strip correction? Trim the image? Apply zero level correction? Apply dark count correction? Apply flat field correction? Apply illumination correction? Apply fringe correction? Convert zero level image to readout correction? Convert flat field image to scan correction? Read out axis (column|line) File describing the bad lines and columns Overscan strip image section Trim data section Zero level calibration image Dark count calibration image Flat field images Illumination correction images Fringe correction images Minimum flat field value Scan type (shortscan|longscan) Number of short scan lines Fit overscan interactively? Fitting function Number of polynomial terms or spline pieces 213 (sample = (naverag= (niterat= (lowrej= (highre= (grow = (mode = 4.3. *) 1) 15) 3.) 3.) 1.) ql) Sample points to fit Number of sample points to combine Number of rejection iterations Low sigma rejection factor High sigma rejection factor Rejection growing radius CCDLIST—What do I got? Normally, if you want to know details of an image, you use the IRAF command IMHEAD. IMHEAD will reveal exposure time, filter number, and the processing state of an image. For example, typing imhead ccd6034 gives the following output. ccd6034[2043,2047][real]: Sa184-9 No bad pixels, no histogram, min=unknown, max=unknown Line storage mode, physdim [2048,2047], length of user area 1013 s.u. Created Wed 23:19:46 25-Jun-97, Last modified Wed 23:19:46 25-Jun-97 Pixel file "HDR\$pixels/ccd6034.pix" [ok] New copy of ccd6034.imh New copy of ccd6034.imh CHIP = ’TEK5’ / DETECTOR NAME TEL = ’LCO-40’ / TELESCOPE NAME UTSTART = ’03 44 00’ / UT OF START FROM PC UTEND = ’03 54 03’ / UT OF END FROM PC FILTERP = 4 / FILTER POSITION FILTER = ’4’ / FILTER NAME CCDPICNO= 6034 / FRAME NUMBER OF IMAGE EXPTIME = 600 / ACTUAL INTEGRATION TIME (S) GAIN = 2 / GAIN NOT NEC. E/DN LOOP = 1 / LOOP SIZE LOOPCTR = 1 / LOOP COUNTER DATE-OBS= ’13Jul96’ / LOCAL DATE OF OBSERVATION RA = ’000000.0’ / RA OBS-ENTERED DEC = ’000000’ / DEC OBS-ENTERED IMTYPE = ’object’ / IMAGE TYPE TRIM = ’Jun 24 18:24 Trim data section is [1:2043,1:2047]’ OVERSCAN= ’Jun 24 18:24 Overscan section is [2050:2064,1:2048] with mean=696 ZEROCOR = ’Jun 24 18:24 Zero level correction image is /gonzo/starcounts/c40 FLATCOR = ’Jun 24 18:24 Flat field image is /gonzo/starcounts/c40jul96/dflat CCDSEC = ’[1:2043,1:2047]’ CCDMEAN = 1567.705 CCDMEANT= 551748001 CCDPROC = ’Jun 25 23:20 CCD processing done’ ILLUMCOR= ’Jun 25 23:19 Illumination image is /home/didjeridu/gonzo/starcoun ITIME = 602.087 214 Note the sections marked OVERSCAN, ZEROCOR, etc. These detail the processing history of the image. The image listed above has had corrections for trim, overscan, bias, flat field and illumination applied. Flipping through a few dozen image headers can get tiresome though, so the process CCDLIST will produce a list of the images in the current directory along with their processing history. You can then type ccdlist ccd*, ccd6031.imh[2043,2047][real][none][B][OTZFI]:Sa184-9 ccd6032.imh[2043,2047][real][none][V][OTZFI]:Sa184-9 ccd6033.imh[2043,2047][real][none][R][OTZFI]:Sa184-9 ccd6034.imh[2043,2047][real][none][I][OTZFI]:Sa184-9 which lists the image name (ccd6031), the size of the image (trimmed to 2043x2047), the pixel status (real), the image type (none), the filter (BVRI, set by a translation file), the processing history (OZTFI) and the image name (SA184-9). The processing history letters stand for: • O = overscan correction applied • T = trim correction applied • Z = bias (zero) correction applied • D = dark correction applied • F = flat field correction applied • I = illumination correction applied The pixel status and image size are read by CCDLIST. Be aware that IRAF automatically converts images to real (floating point) status when running CCDRED processes, which can double the amount of disk space they take up. The image type, filter, and name must be set in the image header. 4.4. Test Images You don’t want to apply any image correction without checking its affects on your images. I usually will copy several CCD frames of various types (a bias, a flat, a few images) into test images (test1, test2, etc.). When I think I have a correction working properly, I apply it to the test images and make sure the results look nice (the eye is very good at this sort of thing) before applying the correction to the entire data set. Go through your data set and select out several images and use the IMCOPY command to copy them into test images. 215 4.5. The Log File It is generally wise to turn on the logfile option in the CCRED processes. The log file will record all the reduction steps you take. This can be very valuable later for reconstructing the reduction when you realize that you screwed up. To use the logfile, set the logfile parameter in any procedure you use to the name of the file you want. Generally, we use the unimaginative title logfile. 4.6. Trimming the Image and Correcting the Overscan Not all images require trimming and overscan correction. In our department, only the Fan Mountain CCD has an overscan. Users of the ST-8 and other CCD’s can skip this section. The Fan Mountain SiTE chip reads out a strip of constant signal (16 to 32 pixels) after each CCD line. Theoretically, this should produce a broad line of constant flux on one edge of your chip. In practice, changes in the voltage of the CCD readout amplifier will cause the signal to vary slightly. Overscan correction fits a function to this strip and thus corrects for voltage variations. When you trim an image, you cut out the sections that are not useful. The overscan section is not useful once you’ve applied the correction, so you can deep-six it. Sometimes, the first or last line in a CCD images will also be useless. It is usually best to do trimming and overscan correction at the same time. The first thing to do is to use IMPLOT to determine which regions of the chip correspond to the overscan and which regions need to be trimmed out. It is probably wisest to do this with flat field frame. 216 The command implot ccd6034 will bring up a plot of the middle line of your CCD chip in a separate window. You probably want to average over a few lines, so type “a:50” in the graphics window to average over 50 lines. Now this plot (Figure 1) will show variations in brightness across these lines. If you used an image frame, you will see large bumps from stars. At the edge of the chip, the signal will fall off dramatically. You will see a spike at the end of the image section and then a drop to a constant level. This constant level is the overscan strip. The spike is garbage. Position the cursor over the edge of the image and hit “e” to expand the view. You want to get a very accurate estimate as to where the overscan region begins. On the image in the figure, the overscan strip is from column 2050 to 2080. Columns 2046 to 2049 are probably garbage and should be cut. You also want to check the other end of the line to make sure you don’t need to cut out low-numbered columns. In this image, they’re fine. You also want to check in the y direction (column) to make sure you don’t need to trim out a few lines. In this image (Figure 2) the y direction is fine. Be aware of what the limits of your chip are. If your chip is 1054 × 512 for example, the signal will go to zero after 512. And remember that not all chips have an overscan region. Open CCDPROC. IRAF uses a notation of [x1:x2,y1:y2]. There are four parameters you need to change. Set overscan and trim to yes. Set trimsec to the area of the image you wish to keep. This is a backwards way of trimming, but it’s the way IRAF is wired. Set biassec to the overscan strip region. In my image, the overscan is over the entire range of y and from 2050 to 2080 in x. Note that it is generally a good idea to avoid the very edge of the image, as well as near column 2048 where the amplifier is ramping down. I want to trim out everything past line 2046. You will also need to fit the overscan region, so change interactive to yes. So my parameters will be: (oversca= (trim = (biassec= (trimsec= (interac= yes) yes) [2050:2080,1:2048]) [1:2046,1:2048]) yes) Apply overscan strip correction? Trim the image? Overscan strip image section Trim data section Fit overscan interactively? Now run CCDPROC on your test images. The only one on which the overscan correction will show is the bias image. Display the unprocessed bias image in one window of XIMTOOL. Then run CCDPROC on its test copy. Typing ccdproc test1 will begin the processing of your image. Since you have set the overscan fitting to interactive, you will be presented with a screen (Figure 3). This will show the variations in the overscan region. They are usually very chaotic but there is an overall trend in the data. It is this broad trend you wish to pluck from the overscan. In these first few images, you will actively fit the overscan. Once you have decided on a function, you will apply it non-interactively to future frames. Within the overscan noise, you should see a solid curve. This curve represents the presently fit function. Use f to refit and plot the function until you do see it. 217 The process of fitting an overscan region is quite complex. You can change the function (spline3 functions do well in general), the order, or the rejection parameters with a colon command (e.g., :order 2 would change the function to second order), then type f to apply the change. Each overscan is unique but there are a few ideas that you should stick to: • You want to fit the broad trend in overscan. If your function follows every little wiggle in the data, it is probably of too high an order and, if used, will create stripes in your images. • Be aware of the scale. If the overscan is only changing by half an ADU, then a simple 2nd order fit may do the trick well. On the other hand, oscillations of several ADU’s should be fit, if they are broad. • Don’t get too fancy. A 15th order function is way too complex. Generally, you want 5th order or less. Only resort to higher orders if there is a gross structure that you must remove. • Sometimes a star landing on or near columns at the edge of the overscan will leak charge into the overscan stripe, creating a spike. It is best to delete (with the d key) the offending points from the graph and interpolate over the region. Bias frames or flat fields will not suffer from this problem. Once you are done fitting the overscan, the image will be trimmed. Display the test image in the second window on XIMTOOL. You should see changes: (1) the image will be smaller, with the edges trimmed off, (2) broad horizontal bands of brightness across the image should be smoothed out. If the brightness bands are not taken care of or new ones appear, you need to try again by recopying the original image onto the test image and CCDPROCing again. Again, be aware of the scale. A brightness fluctuation of half an ADU is no big deal. Once you have decided on good overscan parameters and a good trim section, turn the interactive mode off and run CCDPROC on your bias images. You could now apply it to every image in your data set, but that might double the size of every image—a big problem if your computer disks are cramped. 4.7. Bias Combining and Subtracting CCD images have a bias in them—a reflection of the DC bias voltage applied to the pixels. You need to subtract this out. The overscan correction will subtract out the bulk of it for the Fan Mountain CCD, but one more step is needed. Important Note: If your data was taken over several nights, you will need to process each night’s bias separately. For example, if you observed on two nights, you should have taken a set of bias frames each night. When you combine them, you should combine the biases from night one into one bias image (call it “Night1Bias”) and the biases from night two into another (“Night2Bias”). Keep this in mind while reading the rest of this section. 218 In this section, you will learn to combine images. The bias level on any chip is, by its very nature, noisy. You can improve your image of the bias (and thus, your data) by averaging together a number of bias frames. The IRAF procedure IMCOMBINE is the do-all software for image combining. The default parameters of IMCOMBINE are listed below: input = output = (plfile = (sigma = (logfile= (combine= (reject = (project= (outtype= (offsets= (masktyp= (maskval= (blank = (scale = (zero = (weight = (statsec= (expname= (lthresh= (hthresh= (nlow = (nhigh = (nkeep = (mclip = (lsigma = (hsigma = (rdnoise= (gain = (snoise = (sigscal= (pclip = (grow = (mode = ) ) logfile) average) none) no) real) none) none) Mask 0.) 0.) none) none) none) ) ) INDEF) INDEF) 1) 1) 1) yes) 3.) 3.) ) ) 0.) 0.1) -0.5) 0) ql) List of images to combine List of output images List of output pixel list files (optional) List of sigma images (optional) Log file Type of combine operation Type of rejection Project highest dimension of input images? Output image pixel datatype Input image offsets type Mask value Value if there are no pixels Image scaling Image zero point offset Image weights Image section for computing statistics Image header exposure time keyword Lower threshold Upper threshold minmax: Number of low pixels to reject minmax: Number of high pixels to reject Minimum to keep (pos) or maximum to reject (neg) Use median in sigma clipping algorithms? Lower sigma clipping factor Upper sigma clipping factor ccdclip: CCD readout noise (electrons) ccdclip: CCD gain (electrons/DN) ccdclip: Sensitivity noise (fraction) Tolerance for sigma clipping scaling corrections pclip: Percentile clipping parameter Radius (pixels) for 1D neighbor rejection You will have to set the parameters rdnoise and gain from the statistics for the chip. These should be available from the course instructor. There are several ways to combine. What IRAF does is create an image in which each pixel is the average or median of the corresponding pixels in each input frame. The combine parameter defaults to average. This is probably acceptable. 219 One of the more important aspects of combining is rejecting pixels. Occasionally, a pixel is hot or is struck by a cosmic ray. You want to have IRAF reject pixels that are far removed from the average. You can reject pixels many ways - sigclip, avsigclip. The best, generally, is ccdclip, which uses the noise parameters of your CCD to decide what to reject. The default values for ccdclip are usually acceptable. You should inspect your frames visually to make sure that they are all basically the same. You may also use the IRAF process imstat to get statistics on your frames. The average or midpt of each frame should be about the same. Once you’ve set your parameters and rejected any bad frames, it’s time to combine. Type IMCOMBINE. IRAF will ask you what images you want to combine. You can either manually list all the images (e.g., ccd101, ccd102, ccd103 . . . ) or you can create a list. Creating a list is simple and is very helpful when your are combining a large number of images. You simply create a text file that lists the images you want. You can even add pathnames if you want to combine images from different directories. For example, I might create the list Biaslist which would have the contents: ccd101 ccd102 ccd103 ccd104 \ bias \ ccd105 \ bias \ ccd106 When IRAF asks you for the images to combine, you respond with @filename. In the example above, I would respond with @Biaslist. IRAF will also ask you for the combined file name. Keep it simple. Something like “Bias”. Visually inspect your combined bias frame. It should resemble your other bias frames, only with a much smoother surface. If you are unsatisfied, you can try tinkering with the rejection parameters or switching the combine function to median. Once you are happy with your bias frame, apply it your test, dark and flat field frames. Go into CCDPROC and change zerocor to yes and set zero to your combined bias image (“Bias” in this example). Leave the trim corrections and overscan set, if you used them. You always want to be certain that your images have had all the necessary corrections applied. Remember: If you observed over several nights, you need to match the right bias to the right data. Images taken on the second night of observing should be bias subtracted with the combined bias frame from that night (“Night2Bias”, using the example at the beginning of this section). 220 4.8. Dark Combining and Subtraction Dark current is the data that the CCD receives from itself. The longer a CCD is exposed, the more electrons is accumulates, which are added to the image. Dark frames are becoming rarer and rarer. The Fan Mountain CCD is cooled so that it does not really need them. The ST-8 and other chips can and should have their dark current subtracted at the time of observation as their current is fairly high. However, should you need to process dark frames separately, this will guide you through the process. Essentially, you will do the same thing you did with the bias frames. There is one crucial difference. The level of dark current in each frame is directly proportional to the exposure time. Since you may have various exposure times, you should scale the dark frames by this. The process DARKCOMBINE does this automatically. DARKCOMBINE essentially runs IMCOMBINE in such a way as to create a combined dark. Be sure to change the rdnoise, gain, combine and reject parameters appropriately. Combine your dark images into a frame called “Dark”. Once you have the combined dark frame, run CCDPROC again, this time on your test and flat field frames. Set darkcor to yes and dark to the name of your combined dark frame. 4.9. Flat-Fielding You may take flat fields on the 26-inch and 40-inch by illuminating the surface of the dome and pointing the telescope at it. The 8-inch and 10-inch Meades will never have a flat field screen. If you are using these telescope, you may skip to the section on illumination correction. CCD chips do not respond uniformly to light. Some sections of the chip are more responsive to light than others. This is called a “flat-field” effect as it is most easily exemplified by showing that a uniformly illuminated surface will not appear to be so on the uncorrected CCD frame. To correct for this, you take images of a flat surface (a white screen), combine them, and then divide all your images by the combined flat. Note that the flat field is different for each filter since pixel response is wavelength dependent. Thus, you should start out by dividing your flat field images into directories, one for B filter i mages, one for V, etc. This will help you keep them separate. After you have separated the images, visually inspect them to make sure they look alike. Exposure levels may vary from frame to frame. Once again, you will use IMCOMBINE to add together the flat field frames in each filter. You should combine them into something easy to recognize, e.g., “Bflat” for the B filter flat fields. There is one twist. Your flat fields will not have the same level of exposure. Some recommend scaling them by their exposure time, but I have found this to be ineffective as the lighting level on the flat field screen can change. You should change the scale parameter in IMCOMBINE to median. Flat fielding is the second trickiest part of image reduction. When you are finished, apply the flat field to a test image in that filter using CCDPROC, setting flatcor to yes and flat to the name of your image. Display the test image and its unprocessed original in XIMTOOL. 221 You should note a marked difference between them. The flat field correcton is the most dramatic and most obvious correction to an image that can be applied. There may still be a degree of non-flatness about the field, which will be corrected by illumination correction. Once you are satisfied with the flat field correction, apply it to your test images and all of your data of that filter with CCDPROC. Then go onto the next filter and the next until all your data is flat-fielded. 4.10. Illumination Correction We are now at the last and trickiest part of image reduction—illumination correction. We do illumination correction for two reasons. First, sometimes a flat field is not available. The only flat field that can be found is the sky itself. Second, the flat field is not always evenly illuminated by the flat field lamps. Flat field lamps are not the same color as the night sky and the residual color affects the image at low frequencies. Illumination correction removes these effects as both depend on one basic fact - the only uniform, evenly illuminated surface is the sky. Of course, the sky usually has stars and galaxies in it. We’ll have to get rid of them. The simplest way to produce an illumination flat is to use imcombine to add all your images together in each filter. Thus, stars and galaxies will be rejected when you average the CCD frames. At this point, every image you have should have all the corrections except for illumination applied to them. You now want to go through your entire data set, image by image. You want to make a list, one for each filter, of the images that are “good” for illumination correction. Bad images are those which have extremely bright (and large) stars within them or images with short exposure times. Generally, you want the sky level to be fairly high. Twilight flats are almost always acceptable. Now, you should put the name of each image in a list file, as I suggested with the bias frames. The list should be selective by filter. For example, the list of good sky images in B filter might be called Billumlist and might have the contents: ccd1050 ccd1060 \ f40 \ ccd1062 \ f40 \ ccd1064 Now you will run IMCOMBINE on this image list (giving IRAF the name @Billumlist) when it asks for the combine list). The parameters you used for flat-fielding should be acceptable. The output name should be something like Brough, as this is a rough sky flat, not one smoothed by the process detailed below. Once this image is produced, inspect it. It should produce a nice smooth image that will correct the residual flat-field on your images. Sometimes, I will simply use this image as my 222 illumination correction (all you need do is used HEDIT to add the keyword MKSKYCOR to its header). However, it is usually wise to smooth the image with MKSKYCOR. If your combined sky flat shows bright blobs in it, you probably need to go back and eliminate an image with a bright star in it. Sometimes, you may have to mask out the stars in an image to get a good combined image. I will not detail the masking process here. MKSKYCOR is an IRAF procedure that will take a combined sky frame and apply a boxcar smoothing technique. It is very important that you eliminate any bad columns at this point as they will cause problems with smoothing. The process FIXPIX or IMREPLACE will achieve this. I will not detail the process here. The default parameters of MKYSKYCOR are generally poor for large chips. Change them to read: input = output = (ccdtype= (xboxmin= (xboxmax= (yboxmin= (yboxmax= (clip = (lowsigm= (highsig= (ccdproc= (mode = Brough Bsmooth ) 3.) 0.05) 3.) 0.05) yes) 2.5) 2.5) ) ql) Input CCD images Output images (same as input if none given) CCD image type to select Minimum smoothing box size in x at edges Maximum smoothing box size in x Minimum moothing box size in y at edges Maximum moothing box size in y Clip input pixels? Low clipping sigma High clipping sigma CCD processing parameters Now run MKSYCOR on your unsmoothed image Brough and produce a smooth image Bsmooth. Inspect it. Your image should be a nice clear pattern. If you find small bright or dark rectangles, that is the result of bad pixels contaminating the sample. You need to eliminate them. Once you’ve finalized an illumination image, apply it to your test images in that filter by setting illumcor to yes and illum to your image name. Your images should now be smooth with little variation in the sky across the chip. Once you are satisfied, apply the correction to all the data in that filter. Now you’ve got a reduced data set. Your next tasks will be to calibrate and analyze your images. Always make sure that photometric standard star frames are reduced identically to things you want to calibrate. 223