A Practical Guide to CCD Astronomy

Transcription

1 A Practical Guide to CCD Astronomy PATRICK MARTINEZ AND ALAIN KLOTZ translated by Andre Demers CAMBRIDGE UNIVERSITY PRESS

2 Contents Foreword Preface xiii xvii 1 CCD equipment for astronomy l 1.1 The CCD detector l From photography to CCD l What does a CCD detector look like? Geometric characteristics 4 / -D and 2-D arrays 4 Pixel size 5 The sensitive surface and dead zone of a pixel 6 Color CCDs and black and white CCDs i The number of pixels and the size of the array The operation of the CCD 9 The reading of the CCD 9 The integration of an image CCD performance 14 The sensitivity of a CCD 14 The capacity of a pixel 16 The linearity of a CCD 18 Transfer efficiency 19 The dark current 20 Electroluminescence 23 Defective pixels CCD camera electronics Clock generation 24 The definition of a clock 24 Read time and window mode 28 Binning 28 TDImode 31 Hardware and software sequencers Reading the signal 32 Analog processing of the video signal 32 Analog and digital signals 33 Digitization of the video signal 34

3 1.2.3 The electronic design of a CCD camera Thermal and mechanical aspects General points concerning cooling 38 The need for cooling 38 The production of cold 39 The thermal load Cooling with thermoelectric elements 41 Peltier modules 41 Peltier module characteristics 41 The removal of heat 43 The power supply and temperature regulation of Peltier modules The problem of frost The camera body The computer environment The computer Software 52 Acquisition software 52 Image processing and display software 53 CCD camera characteristics and performance Geometric characteristics The number of pixels The shape and size of pixels Electronic and thermal characteristics Read-out noise 59 The origin of read-out noise 59 The influence of read-out noise The thermal load and noise Sensitivity to interference Levels of digitization Photometric characteristics The capacity of pixels Sensitivity and detection thresholds Photometric precision 72 Photon noise 72 The evaluation of photometric precision The precision and linearity of the converter CCD quality Acquisition functions 77

4 2.5.1 Exposure Automatic mode Read-time Windowing Binning Types of shutter Planetary image acquisition TDI mode User friendliness Automatic guiding 86 3 Image production The camera mounting Choice of optical combinations 88 The resolution 88 The field of view Mechanical integration The chromatic aberration of refractors Guiding problems The filter assembly The mounting for TDI mode The first images Pointing the telescope Focusing Photometric correction of images Dark acquisition Flat field acquisition A night of observations Display and image analysis functions The concept of the CCD image The image on the CCD detector The image in memory The screen image The image on disk The screen copy Display functions Classic display Blink display 128

5 4.2.3 True color display Isophote display Polarization card display Cross-sectional display Perspective display Analysis functions Display help Photometric analysis Photocenter calculation 135 Image processing functions Image processing Preprocessing The bias image Dark subtraction 139 The classic method 139 The generic dark method 140 The dark optimization method 140 The nonlinearity of darks The flat field division Cosmetic corrections Preprocessing automation Point to point operations Arithmetical operations Statistical point to point operations Transformations in color space Transformations in polarization space Geometric transformations Translations, rotations, and mosaics 155 Translations 155 Rotations 156 Mosaics 156 Permutation Enlargements and reductions Anamorphs Convolutions Spatial convolutions 162 High-pass filters 162 Low-pass filters 164

6 The unsharp mask technique 165 Morphological filters Frequency convolutions 167 Fourier transformations 168 Convolutions in Fourier space Image restoration Direct algorithms The Van Cittert algorithm The Lucy-Richardson algorithm The maximum entropy algorithm Diverse algorithms Application areas for different methods Modeling Stellar modeling Isophotal modeling Modeling of the sky background Choosing image processing software 182 CCD applications in astronomy The advantages of the CCD Image quantification and linearity Detectivity Spectral sensitivity l.4 Real time work A restriction: the wide field High resolution work Planetary surfaces 187 Image acquisition 188 Basic image processing 190 Use of data 190 Filtering of planetary images Double stars 195 Image acquisition 196 Data reduction The Sun Images and detection of faint objects The field of study Image acquisition Multiple exposures and tracking comets Image processing and analysis 205

7 6.4 Photometry Areas of application Stellar photometry 210 The use of filters 210 The magnitude constant 212 Absolute magnitude calibration 213 The use ofaavso and AFOEV maps Photometry of extended objects 219 Integral photometry - comets 219 Surface photometry - galaxies Rapid photometry Astrometry Areas of application Image acquisition and analysis Alleviating the field problem Spectrography Areas of application Wavelength calibration Chromatic calibration Factors limiting performance Analysis software Example application Sky surveillance The area of study Limited zone searches 231 Supernova searches 231 The rediscovery of periodic comets Extended zone searches A particular case - TDI mode 236 Conclusion 238 Bibliography 239 Index 241