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Very Long Baseline Interferometry Techniques and Applications NATO ASI Series Advanced Science Institutes Series A Series presenting the results of activities sponsored by the NA TO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The Series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division A Life Sciences Plenum Publishing Corporation B Physics London and New York C Mathematical Kluwer Academic Publishers and Physical Sciences Dordrecht, Boston and London o Behavioural and Social Sciences E Applied Sciences F Computer and Systems Sciences Springer-Verlag G Ecological Sciences Berlin, Heidelberg, New York, London, H Cell Biology Paris and Tokyo Series C: Mathematical and Physical Sciences -Vol. 283 Very Long Baseline Interferometry Techniques and Applications edited by Marcello Felli Arcetri Observatory, Florence, Italy and Ralph E. Spencer University of Manchester, Jodrell Bank, U.K. Kluwer Academic Publishers Dordrecht / Boston / London Published in cooperation with NATO Scientific Affairs Division Proceedings of the NATO Advanced Study Institute on The Techniques and Applications of Very Long Baseline Interferometry Castel S. Pietro Terme, Bologna, Italy September 12-23, 1988 Library of Congress Cataloging In Publication Data NATO Advanced Study Institute on VLBI (1988 : Bologna, Italy) Very long baseline interferoNetry techniques and applications proceedings of the NATO Advanced Study Institute on VLBI, Castel S. Pietro Terme, Bologna, Italy, 12-23 September, 1988 I edited by Marcello Felli and Ralph E. Spencer. p. CM. -- (NATO ASI series. Series C, MatheNatical and physical sciences; no. 283) 'Published in cooperation with NATO Scientific Affairs Division." Inc 1u des index. 1. Very long baseline lnterferometry--Congresses. I. Felli, Marcello. II. Spencer, Ralph E. III. North Atlantic Treaty Organization. Scientific Affairs Division. IV. Title. V. Series. QB479.3.N37 1988 522' . 682--dc20 89-15317 ISBN-13: 978-94-010-7595-4 e-ISBN-13: 978-94-009-2428-4 001: 10.1007/978-94-009-2428-4 Published by Kluwer Academic Publishers, P.O. Box 17,3300 AA Dordrecht, The Netherlands. Kluwer Academic Publishers incorporates the publishing programmes of D. Reidel, Martinus Nijhoff, Dr W. Junk and MTP Press. Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers, 101 Philip Drive, Norwell, MA 02061, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers Group, P.O. Box 322, 3300 AH Dordrecht, The Netherlands. Printed on acid free paper All Rights Reserved © 1989 by Kluwer Academic Publishers Softcover reprint of the hardcover 1s t edition 1989 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photo copying, recording or by any information storage and retrieval system, without written permission from the copyright owner. TABLE OF CONTENTS Preface ix List of Participants xi PART 1 FUNDAMENTAL VLBI TECHNIQUES 1. Basic Radio Astronomy Bryan Anderson 3 2. Fundamentals of Interferometry Ralph E. Spencer 11 3. Introduction to VLBI James M. Moran 27 4. The Effects of Propagation on VLBI Observations James M. Moran 47 5. Signal Flow at VLBI Antennas Bryan Anderson 61 6. An Introduction to Closure Phase and Self-Calibration Peter N. Wilkinson 69 PART 2 VLBI TECHNIQUES IN PRACTICE 7. Scheduling, Correlating and Postprocessing of VLBI Observations Walter Aiel 97 8. Calibration Methods R. Craig Walker 141 VI 9. Sensitivity R. Craig Walker 163 10. An Introduction to Deconvolution in VLBI Peter N. Wilkinson 183 11. Mapping in Practice Lars B. Baath 199 12. Spectral Line VLBI Philip Diamond 231 13. Introduction to Phase-Reference Mapping Walter Ale! 261 14. Polarimetry William Cotton 275 15. Geodesy VLBI Observables Bernt Ronnang 289 PART 3 SOME RESULTS IN VLBI 16. Geodesy, Geodynamics and Astrometry using VLBI Bernt Ronnang 305 17. Recent Results in Astronomy I: Extragalactic Lucia Padrielli 319 18. Recent Results in Astronomy II: Pulsars and Stars Bryan Anderson 339 19. Recent Results in Astronomy III: Interstellar Masers Philip Diamond 345 vii PART 4 THE PRESENT AND FUTURE OF VLBI 20. The European and U.S. VLBI Networks in 1988 Richard T. Schilizzi 357 21. Comparison with other Instruments Carla Fanti 363 22. VLBI in the 1990's Richard T. Schilizzi 397 PART 5 CONTRIBUTED PAPERS List of Contributions 421 APPENDIX Call for proposals 427 Current Data on Telescopes of the European Network 431 INDEX 435 Preface The quest for high resolution has preoccupied radio astronomers ever since radio waves were first detected from space fifty years ago. This venture was par ticularly stimulated by the discovery of quasars, and led to the development of interferometer techniques using baselines of transglobal dimensions. These meth ods have become known as Very Long Baseline Interferometry (VLBI). Arrays of radio telescopes situated all over the Earth (or even in space) are regularly used for researches in radio astronomy, reaching resolutions as small as a fraction of a milli arcsecond. The technique also allows the measurement of the positions of the radio telescopes to a few millimeters and so VLBI has become a major tool in geodesy and the study of the rotation of the Earth. VLBI has now passed the pioneer stage and is becoming a standard facility available to astronomers and geodesists, requiring the coordination of the operations of indpendently owned radio telescopes around the world. In Europe observatories from England, Federal Republic of Germany, France, Italy, Poland, Sweden and The Netherlands are coordinated in their VLBI activity by the European VLBI Network Consortium (EVN). The Programme Committee of the EVN allocates time to scientific projects on a routine basis three times a year. The Unites States has a similar arrangement of a network of independent radio observatories, and joint experiments using 'Global Network' are often made. Despite the enormous progress in the technique over recent years, there is still a limited number of astronomers using VLBI. The members of the EVN Consortium felt that a Summer School on VLBI Techniques would be the most appropiate way to achieve the goal of a wider group of users. The summer school, sponsored by NATO as an Advanced Study Institute, was held in Castel S. Pietro Terme on 12-23 September 1988. Lectures were given on topics ranging from an introduction to the basis of radio astronomy to the more esoteric aspects of imaging and analysis for geodesy. These proceedings reflect the fact that the Institute was primarily pedagogical, its main goal being to provide the non experts with a detailed description of all the aspects of VLBI, from the basic theory to the details of its application. For the first time one can find in a single text all the information needed to start from scratch a new VLBI scientific project. Furthermore, part of the material contained here has not appeared elsewhere. The reader should note that the lectures were self-contained and given by separate individuals. With this choice some degree of repetition was inevitable. However, this was not felt to be educationally detrimental as repetition with a different slant can improve understanding. ix x In editing we have taken the liberty of rearranging the order in which the talks were given to give a more structured appearence to the proceedings. Part 1 contains introductory material, starting with an outline of the basic priciples of radio astronomy and interferometry followed by a fuller decription of VLBI. An impromptu talk on signal flow paths in VLBI receiver systems was re quested by the students and so a written-up version is included here. The section ends with an introduction to the properties which makes VLBI imaging possible, that is 'closure'. Part 2 contains the more detailed aspects of VLBI analysis including a useful description of how to process VLBI data at the correlator, methods of calibration and how to make maps. The last few lectures in the section are on the more advanced analysis topics. Part 3 summarizes recent results arising from the application of VLBI to geodesy and extragalactic and galactic astronomy. Part 4 contains talks on the VLBI networks and radio telescopes currently in use around the world and ends with a discussion of future plans. A list of contributed papers is given in Part 5, and finally the Appendix contains technical information of use to the scientific proposal writer. The neophyte in VLBI should perhaps read Part 3 first to see how VLBI can help his/her astronomical researches, followed by Part 1 in order to get a basic understanding of the technique. Part 4 will tell him/her how to obtain telescope time, and if succesful the intrepid VLBl's should now tackle Part 2. The Editors wish to thank the following: the members of the EVN Programme Committee and the EVN Directors for their continued encouragment, the Local Organizing Committee for their unstinting efforts before and during the Institute, the Italian CNR for funds to help with travel for non-NATO partecipants, the NATO Science Committe of the Advanced Study Institute programme for providing the means by which the summer school and these proceedings have become possible, the students for contributing so much to the discussion and last but by no means least the lecturers for their hard work and dedication throughout the summer school. Directing the summer school and editing its proceedings was a hard and time consuming job. If this book will be able to assist newcomers in this field and enlarge the number of VLBI users we have reached our goal. Marcello Felli, Arcetri Observatory ~ Ralph E. Spencer, University of Manchester ~ l-J March, 1989 ::0 o ~ <"7 c\ ~, }..O * Participants Directors of Institute Marcello Felli Ralph E. Spencer Osservatorio di Arcetri University of Manchester Largo E. Fermi 5 Jodrell Bank 50125, Firenze Macclesfield SKll 9DL Italy United Kingdom Local Organizing Committee Roberto Ambrosini Franco Mantovani Istituto di Radioastronomia Istituto di Radioastronomia Via Irnerio 46 Via Irnerio 46 40126 Bologna 40126 Bologna Italy Italy Luisa Baldeschi Lucia Padrielli Istituto di Radioastronomia Istituto di Radioastronomia Via Irnerio 46 Via Irnerio 46 40126 Bologna 40126 Bologna Italy Italy William Junor Paolo Tomasi Istituto di Radioastronomia Istituto di Radioastronomia Via Irnerio 46 Via Irnerio 46 40126 Bologna 40126 Bologna Italy Italy xi
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