Astrophysical Techniques Fourth Edition C R Kitchin University of Hertfordshire Observatory Institute of Physics Publishing Bristol and Philadelphia # IOP Publishing Ltd 2003 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. Multiple copying is permitted in accordance with the terms of licences issued by the Copyright Licensing Agency under the terms of its agreement with Universities UK (UUK). C R Kitchin has asserted his moral rights under the Copyright, Designs and Patents Act 1998 to be identified as the author of this work. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN 0 7503 0946 6 Library of Congress Cataloging-in-Publication Data are available First edition 1984, reprinted 1988 Second edition 1991, reprinted 1998 Third edition 1998, reprinted 2002 Commissioning Editor: John Navas Production Editor: Simon Laurenson Production Control: Sarah Plenty Cover Design: Fre´de´rique Swist Marketing: Nicola Newey and Verity Cooke Published by Institute of Physics Publishing, wholly owned by The Institute of Physics, London Institute of Physics Publishing, Dirac House, Temple Back, Bristol BS1 6BE, UK US Office: Institute of Physics Publishing, The Public Ledger Building, Suite 929, 150 South Independence Mall West, Philadelphia, PA 19106, USA Typeset by Academic þ Technical, Bristol Printed in the UK by MPG Books Ltd, Bodmin, Cornwall For Christine Contents Standardsymbols Preface 1Detectors 1.1Opticalandinfrareddetection Introduction Detectortypes Theeye Semiconductors Thephotoelectriceffect Adetectorindex Detectorparameters Cryostats Charge-coupleddevices(CCD) Photography Photomultipliers Superconductingtunneljunctiondetectors(STJs) Othertypesofdetector Photovoltaiccells Thermocouples Phototransistors Chargeinjectiondevices(CID) Televisiontubes Imageintensifiers Infrareddetectors Photoconductivecells Bolometers Othertypesofdetector Ultravioletdetectors Futurepossibilities Noise Intrinsicnoise Signalnoise Digitization Telescopes Opticaltheory Telescopedesigns Background Designs Telescopesinspace Mountings Real-timeatmosphericcompensation Samplingsystem Wavefrontsensing Wavefrontcorrection Futuredevelopments Observingdomes,enclosuresandsites Exercises 1.2Radioandmicrowavedetection Introduction Detectorsandreceivers Radiotelescopes Construction Exercises 1.3X-rayandgamma-raydetection Introduction Detectors Geigercounters Proportionalcounters Scintillationdetectors Gasscintillationproportionalcounters Chargecoupleddevices Superconductingtunneljunctiondetectors Comptoninteractiondetectors Sparkdetectors Cˇ erenkovdetectors Solid-statedetectors Microchannelplates Nuclearemulsions Shielding Imaging Collimation Coincidencedetectors Occultation Reflectingtelescopes Resolutionandimageidentification Spectroscopy Gratingspectrometers Braggspectrometers Background Thespectrometer Polarimetry Observingplatforms 1.4Cosmicraydetectors Background Detectors Real-timemethods Cloudchamber Geigercounters Proportionalcounters Sparkdetectors Flashtubes Scintillationdetectors Cˇ erenkovdetectors Background Detectors Solid-statedetectors Nucleondetectors Residualtrackdetectors Photographicemulsions Ionizationdamagedetectors Indirectdetectors Electroscope 100MeVgammarays Diffuseradioemission Fluorescence Solarcosmicrays Carbon-14 Arrays Correctionfactors Atmosphericeffects Solareffects Terrestrialmagneticfield Exercises 1.5Neutrinodetectors Background Chlorine-37detectors Water-baseddetectors Gallium-baseddetectors Scintillator-baseddetectors Othertypesofdetector Direct-interaction-typedetectors Geologicaldetectors Currentlyoperatingandplannedneutrinodetectors Exercises 1.6Gravitationalradiation Introduction Detectors Directresonantdetectors Direct,non-resonantdetectors Indirectdetectors Exercises 2Imaging 2.1Theinverseproblem Deconvolution 2.2Photography Introduction Structureofthephotographicemulsion Thephotographicimage Processing Hypersensitization Heating Gasimmersioneffects Filmtypes Techniquesofastronomicalphotography Analysisofphotographicimages 2.3Electronicimaging Introduction Televisionandrelatedsystems Imageintensifiers Magneticallyfocusedimageintensifiers Electrostaticallyfocusedimageintensifiers Proximityfocusedimageintensifiers Cascades Recording Photoncountingimagingsystems 2.4Scanning 2.5Interferometry Introduction Michelsonopticalstellarinterferometer Michelsonradiointerferometer Reflectioninterferometers Aperturesynthesis Intensityinterferometer Exercises 2.6Speckleinterferometry 2.7Occultations Background Techniques Analysis 2.8Radar Introduction Theoreticalprinciples Equipment Dataanalysis Meteors Exercise 2.9Electronicimages Imageformats Imagecompression Imageprocessing Greyscaling Imagecombination Spatialfiltering 3Photometry 3.1Photometry Background Filtersystems Stellarparameters Exercises 3.2Photometers Instruments Observingtechniques Datareductionandanalysis Exercise 4Spectroscopy 4.1Spectroscopy Introduction Diffractiongratings Prisms Interferometers Fibreoptics Exercises 4.2Spectroscopes Basicdesignconsiderations Prism-basedspectroscopes Gratingspectroscopes Integralfieldspectroscopy Multi-objectspectroscopy Techniquesofspectroscopy Futuredevelopments Exercises 5Othertechniques 5.1Astrometry Introduction Background Transittelescopes Photographiczenithtubeandtheimpersonalastrolabe Micrometers Astrographsandothertelescopes Interferometers Space-basedsystems Detectors Measurementandreduction Skysurveysandcatalogues Exercises 5.2Polarimetry Background Opticalcomponentsforpolarimetry Polarimeters Spectropolarimetry Datareductionandanalysis Exercises 5.3Solarstudies Introduction Solartelescopes Spectrohelioscope Narrowbandfilters Coronagraph Pyrheliometer Solaroscillations Othersolarobservingmethods Exercise 5.4Magnetometry Background Magnetometers Datareductionandanalysis 5.5ComputersandtheWorldWideWeb Introduction Digitalskysurveys Virtualobservatories Appendices 1Northpolarsequence 2Juliandate 3Answerstotheexercises 4Acronyms 5Bibliography Standard symbols Most of the symbols used in this book are defined when they are first encoun- tered and that definition then applies throughout the rest of the section con- cerned. Some symbols, however, have acquired such a commonality of use that they have become standard symbols among astronomers. Some of these are listed below, and the symbol will not then be separately defined when it is encountered in the text. amu atomic mass unit ¼ 1:6605 Â 10ÿ27 kg ÿ1 c velocity of light in a vacuum ¼ 2:9979 Â 108 ms e charge on the electron ¼ 1:6022 Â 10ÿ19 C eÿ symbol for an electron eþ symbol for a positron eV electron volt ¼ 1:6022 Â 10ÿ19 J G gravitational constant ¼ 6:670 Â 10ÿ11 Nm2 kgÿ2 h Planck’s constant ¼ 6:6262 Â 10ÿ34 Js k Boltzmann’s constant ¼ 1:3806 Â 10ÿ23 JKÿ1 ÿ31 me mass of the electron ¼ 9:1096 Â 10 kg n symbol for a neutron pþ symbol for a proton U, B, V magnitudes through the standard UBV photometric system 12 6C symbol for nuclei (normal carbon isotope given as the example); the superscript is the atomic mass (in amu) to the nearest whole number and the subscript is the atomic number symbol for a gamma ray ÿ12 ÿ1 "0 permittivity of free space ¼ 8:85 Â 10 Fm symbol for wavelength symbol for refractive index (also, n is widely used) ÿ7 ÿ1 0 permeability of a vacuum ¼ 4 Â 10 Hm symbol for frequency (also, f is widely used). Preface The aim of this book is to provide a coherent state-of-the-art account of the instruments and techniques used in astronomy and astrophysics today. Whilst every effort has been made to make it as complete and up-to-date as possible, the author is only too well aware of the many omissions and skimpily treated subjects throughout the work. For some types of instru- mentation it is possible to give full details of the instrument in its finally developed form. However, for the ‘new astronomies’ and even some aspects of established fields, development is occurring at a rapid pace and the details will change between the writing and publishing of this edition. For those areas of astronomy therefore, a fairly general guide to the principles behind the techniques is given and this should enable the reader to follow the detailed designs in the scientific literature. With this fourth edition, many new instruments and techniques are included for the first time, and some topics have been eliminated on the grounds that they have not been used by either professional or amateur astronomers for many years. Other topics, while no longer employed by professional observers for current work, are included because archive material that is still in use was obtained using them and/or because amateur astronomers use the techniques. A few references to web sites have been included but not many because the sites change so frequently and search engines are now so good. However, this resource is now the point of first call for most scientists when they have a query, and much material, such as large sky surveys, is only available over the web. Further- more it is used for the operation of some remote telescopes and it forms the basis of ‘virtual’ telescopes as discussed in the last chapter. Another aim has been to try to reduce the trend towards fragmentation of astronomical studies. The new techniques that are required for observing in exotic regions of the spectrum bring their own concepts and terminology with them. This can lead