Ian S, McLean Electronic Imaging in Astronomy Detectors and Instrumentation (Second Edition) j""v Published f udiisnea in association with witn fyj Springer Praxis PubUshing Publisl PR Chichester, UK
Contents About the author.. '..:...' xv Preface xvii List of figures. xxi List of tables.. xxix List of abbreviations and acronyms xxxi Introduction.... xxxvii 1 The development of electronic imaging in astronomy 1 1.1 Observational astronomy... 1 1.1.1 Historical development '... 1 1.1.2 What are the observables? :...-... 7 "1.2 From eyes to electronic sensors 10 1.2.1 The eye 11 1.2.2 Photography 13 1.2.3 The photoelectric effect 15 1.2.4 Photomultiplier tubes 15 1.2.5 Electron-scanning devices....- -.. 17 1.3 The impact of solid-state imaging 19 1.3.1 Invention of the CCD 19 1.3.2 Electronic imaging across the spectrum 22 1.4 The continuing growth of astronomical technology... 25 1.4.1 Bigger telescopes and better images^ 25 1.4.2 Common-user instrumentation and automation... 26 1.4.3 Surveys and data archives; the virtual observatory... 27
vi Contents 1.5 Terminology of electronic imaging... 29 1.5.1 Image formation.. 29 1.5.2 Detector performance 32 1.6 Summary. 34 1.7 Exercises 35 1.8 References 36 Web sites.. : 36 1.9 Suggestions'for. additional reading...].. 37 2 Beating the atmosphere 39 2.1 Atmospheric absorption and transmission : 39 2.2 Atmospheric emission, thermal and non-thermal 43 2.3 Turbulence......' 46 2.3.1 Kolmogorov theory and origin of seeing 48 2.3.2 Fried parameter 51 2.3.3 Speckle interferometry 53 2.3.4 Lucky imaging 53 2.4 Adaptive optics 54 2.4.1 Measuring the wavefront.. 54 2.4.2 The isoplanatic patch 58 2.4.3 Deformable mirrors. 59 2.4.4 Natural guide star systems 60 2.4.5 Laser guide star systems 63 2.5 Optical and IR interferometers...'... 66 2.5.1 Phase closure 70 2.6 Space telescopes 71 2.7 Summary 72 2.8 Exercises. 73 2.9 References 74 Web sites -.75 3 Telescopes 77 ~" 3.1 Historical development... 77 3.2 Telescope designs 84 3.2.1 Basic optical properties. 84 3.2.2 The astronomical (lens) telescope.."..' 87 3:2.3- Reflecting telescopes; the parabolic dish. :. 90 3.2.4 Correctors and hybrid telescopes 93 3.2.5 Telescope mounts 94 3.3 Automated telescopes and remote observing '. 97 3.3.1 Remote observing 97 3.3.2 Automated imaging telescopes 98 3.3.3 Survey telescopes.... ". 101
Contents vii 3.4 Very Large Telescope design.. 102 3.4.1 Segmented primaries 102 3.4.2 Thin-meniscus mirrors 105 3.4.3 Spin-cast honeycombs... ; 108 3.4.4 Prospects for Extremely Large Telescopes 110 3.5 Case study: design of a two-mirror telescope Ill 3.6 Summary... 114 3.7 Exercises 115. 3.8 References " 116 Web sites... 117 4 ' The discovery power of modern astronomical instruments 119 ' 4.1 Imaging the sky; more than pictures 119 4.1.1, Early surveys of the sky 121 4.1.2 Digitized surveys 123 4.1.3 Drift scanning and the Sloan Digital Sky Survey 129 ' 4.1.4 The Two Micron All Sky Survey... 130 4.1.5 Deep imaging in selected fields, 132 4.1.6 Diffraction-limited imaging 133 4.1.7 Interferometers; expanding the baseline 134 4.2 Spectroscopy; atomic fingerprints 135. 4.2.1 Introduction... 135 4.2.2 High resolution, from cosmic abundances to planet hunting 138 4.2.3 Medium-resolution and low-resolution spectroscopy... 142 4.2.4 Multiobject spectroscopic surveys; 3-D maps of the (. j" Universe 144 4.2:5 Imaging spectroscopy; x, y, and A 150 " t r 4.3 Polarization; transverse waves 152 4.3.1 Introduction 152 4.3.2 Polarization maps and spectra 153 4.4 Summary 155 4.5 Exercises 156 4.6 References 157 '" General astronomy texts referenced 159 Web sites 159 5 Instrumentation and detectors 161 - * 5.1 Photometers and cameras. 161 5.1.1 Photoelectric photometers... 161 5.1.2 Camera systems 163 5.1.3 Pixel sampling and matching to the plate scale... 164
viii Contents " * '. 5.2. Spectrometers....; 167 5.2.1 Resolution and dispersion.. 168 5.2.2 Diffraction gratings...:... 168 5.2.3 ' Prisms '. 175 :.' ' 5.2.4 Grisms.., 176 5.3 Polarimeters...' 177 5.3.1 Modulators and polarizers... - 177 5.3.2 The Stokes parameters...." :... :.... 178 5.3.3 Mueller matrices.'..., 180 5.4 Interferometers -...'.. 181 5.4.1 The Fourier Transform Spectrometer (FTS) 181 5.4.2 The Fabry-Perot etalon.. :. 182 5.4.3 Interference filters ".... 183 5.5 Detectors...'....-...;..- 184 5.5.1 Classification..-' 184 5.5.2 Semiconductors.. :. 186 5.5.3 Photoconductors and photodiodes.. 191 5.5.4 Thermal detectors._... 194 5.5.5 Coherent detectors. 195 5.6, Summary 195 5.7 Exercises...; 196 5.8 References and suggested further reading 197 Designing and building astronomical instruments 199 6.1 Basic requirements... 199 6.2 Overall system layout. \ 200 6.3 Optical design,. 201 6.3.1 First order to ray tracing.. 201 6.3.2 Aberrations 203 6.3.3 Wavefront errors 207 6.3.4 Coatings and interference filters 211 6.4 Mechanical design..... 212 6.4.1 Materials and properties.. 213 6.4.2. Mechanisms... 216 6.5 Cryogenics and vacuum methods 218 6.6 Electronics design. '. 228 6.7 Software 235 6.8 Summary......!.-.-. 237 6.9 Exercises...-...-. -... 237 Special topic.... : :. 239 6.10 References and suggested further reading )....... '... 239 Web sites for optical software.;... 240
Contents ix 7 Charge-coupled devices 241 7.1 The early years 241 7.1:1 Invention and development 241 7.1.2 The astronomical push 242 7.2 "Basic principles, of CCDs,' 248 7.2.1 Charge storage.. 248 7.2.2 Charge-coupling and clocking 252 7.3 CCD constructions 254 7.3.1 Interline and frame-transfer CCDs 254 7.3.2 CCD outputs...:... 256. 7.3.3 Buried-channel CCDs. 257 7.3.4 Two-phase, four-phase, and virtual-phase CCDs 260 7.3.5, Backside-illuminated CCDs 261 7.3.6 Multi-pinned phase CCDs 262 7.4 Astronomical requirements :... 264 7.4.1 Slow-scanning, cooling, and optimization... 264 7.4.2 CCD mosaics.. r 265 7.4.3 Drift scanning '...: ;266.\. 7.5 Special devices 268 7.5.1 High-speed CCDs with on-chip gain. 268 7.5.2 Deep-depletion CCDs for no fringing... : 270 7.5.3 Orthogonal transfer CCDs. 271?.5.4. Customized CCDs 272. 7.6 Summary.273 7.7 Exercises.. 273 7.8 References and suggestions for further reading - 274 Web sites 275 CCDs forcollege teaching -...' 275 8 Practical operation of CCDs :. 277 8.1 Clock voltages and basic electrical factors.,. 277 8.1.1 The analog signal chain 279 8.1.2 CCD sequencers and clock drivers. 280 8.2 Dark current and cooling 287 8.3 ' Cosmic rays and luminescence 290 8.4 Bad pixels and charge transfer efficiency.. 292 8.5 Noise sources! 296 8.6 Signal processing and digitization..- 298 8.6.1 Correlated double-sampling 300 8.6.2 On-chip binning 304 8.6.3 Overscanning and sub-arrays 305 8.7 Uniformity of response. 306 8.8 UV flashing and QE pinning 307
x Contents 8.9 Summary... v 311 8.10 Exercises. 311 8.11 References and suggested further reading. : 312. Web sites. 313 9 Characterization and calibration of array instruments. 315 9.1 From photons to microvolts : 315 9.1.1 Quantum efficiency and DQE 316 9.1.2 Photon transfer function. 319 9.2 Noise, bias, and dark current 323 9.3 Flat-fielding strategies. -. 325 9.4 Fringes and sky emission 331 9.5 Linearity.. 331 9.6 Photometry :... 332 9.7 Spectroscopy... 340 9.8 Polarimetry 343 9.9 Signal-to-noise calculations 343 9.10. Summary 350 9.11 Exercises 350 9.12 References.., 351 Web sites " ;. 352 10 Image processing and analysis 353 10.1 Computers.*....;.. "353 10.1.1 Data acquisition and data transfer... 353 10.1.2 Data file formats. 356 10.2 Data reduction and analysis systems. 358 10.2.1 The IRAF package 361 10.2.2 The IDL package 366 10.2.3 FITS Liberator 369 10.3 Principles of image analysis and processing. 369 10.3.1 Displaying images 369 10.3.2 Image enhancement.'. 374 10.4. Image restoration...:.. 378 10.5 Summary 382 10.6 Exercises. 383 10.7 References...;:. 383 Web sites 384 11 Electronic imaging at infrared wavelengths : 385 11.1 Introduction..-.. :.. :-...'. 385 11.1.1 Early history of infrared astronomy.. 386 11.1.2 The beginning of modern infrared astronomy... 387 11.1.3 The launch of IRAS :... 389
Contents xi 11.2 Infrared wavebands 389 11.2.1 Atmospheric windows 389 11.2.2 The high-background problem 391-11.2.3 Chopping... : 391. 11.3 Infrared array detectors 393 11.3.1 The infrared "array" revolution, dejd vu.- 393 11.3.2 The hybrid structure 397 11.3.3 Photovoltaicdevices 400 11.3.4 Impurity band conduction devices 401 11.3.5 Far-infrared arrays based on germanium 403 11.3.6 Other forms of infrared arrays. 404 11.4 Practical operation of infrared arrays 405 11.4.1 Linearity ~"" 405 11.4.2 Dark current'and cooling.406 11.4.3. Noise sources 407 11.4.4 Quantum efficiency 408 11.4.5 Multiple outputs 408 11.4.6 Array controllers 408 11.5 Readout modes 410 11.5.1 Single-sampling 412 11.5.2 Correlated double-sampling (CDS) 413 11.5.3 Reset-read-read or Fowler sampling 413 11.5.4 Sampling up the ramp (UTR) 415 11.6 Infrared instruments 415 11.6.1 General issues...-...' 415 11.6.2 IR cameras 416 11.6.3 Infrared spectrometers. 417 11.6.4 AO cameras and integral field spectroscopy 419 11.7 The impact of infrared arrays 420 11.7.1 Ground-based observing 420 11.7.2 The Stratospheric Observatory for Infrared Astronomy. 421 11.7.3 IR astronomy in space 423 11.8 Summary ;...' 425 11.9 Exercises 426 11.10 References 426 Web sites 429 12 Electronic imaging at ultraviolet, X-ray, and gamma-ray, wavelengths... 431 12.1 Introduction..:... 431 12.1.1 Grazing incidence telescopes 432 12.1.2 Coded mask telescopes. 435 12.2 Ultraviolet detectors and instruments 437 12.2.1 UV-sensitive CCDs 440. 12.2.2 MicroChannel plates 441 12.2.3 Electron-bombarded CCDs 445
xii Contents. : 12.3 X-ray detectors and instruments 446 12.3.1 Introduction 446 12.3.2 CCDs in the X-ray regime... ;., 448 12.3.3 X-ray spectroscopy 450 12.3.4 X-ray instruments: the Chandra X-ray Observatory (CXO), 451 12.4 Gamma rays 453. 12.4.1 Detectors for high energy 454 12.4.2 Gamma-ray observatories in space 457 12.4.3 Ground-based gamma-ray observatories.. 461 12.5 Summary 462 12.6 Exercises.. 463 12.7 References ; 463 Web sites....'.. 464 Suggested further reading 465 13 Electronic imaging at sub-millimeter and radio wavelengths. 467 13.1 Introduction to radio astronomy 467 13.2 Radio telescopes '.. 471 13.2.1 Antennas \. 471 13.2.2 Receivers 474 13.2.3 Detectors/Mixers _,..480 13.2.4 Interferometers and aperture synthesis 481 13.3 The microwave background 485 13.3.1 COBE and WMAP...: 486 13.4 Sub-millimeter detectors and instruments 489 13.4.1 Bolometers 490 13.4.2 Thermal edge sensors!.:...-.: 493 13.4.3 Microwave kinetic induction detectors : 495 13.5 Summary :...'.... 496 13.6 Exercises. 497 13.7 References and sugested further reading 498 Web sites..... ; -499 14 Future developments...., 501 14.1 Scientific challenges 501 14.2 New ground-based telescopes 502 14.3 Next-generation adaptive optics 507 14.4 Next-generation instrumentation 508 14.5 New space telescopes v.. :. :. 509 14.6 The future of electronic imaging.... 511 14.7 Conclusion :... 512 14.8 References..:...,.. 513 Web sites...:: 513
Contents xiii Answers to selected exercises 515 APPENDICES A Powers-of-10 notation.. 521 B Units of measurement and useful conversions 523 C Physical and astronomical constants 527 D Astronomical magnitude scale and relation to lux 529 E Basic observational astronomy facts 531 F Useful statistics 535 Index :. 537