EXOPLANET OBSERVING FOR AMATEURS Second Edition (plus) Bruce L. Gary Books by Bruce L. Gary ESSAYS FROM ANOTHER PARADIGM, 1992, 1993 (Abridged Edition) GENETIC ENSLAVEMENT: A CALL TO ARMS FOR INDIVIDUAL LIBERATION, 2004, 2006, 2008 THE MAKING OF A MISANTHROPE: BOOK 1, AN AUTOBIOGRAPHY, 2005 A MISANTHROPE’S HOLIDAY: VIGNETTES AND STORIES, 2007 EXOPLANET OBSERVING FOR AMATEURS (First Edition), 2007 QUOTES FOR MISANTHROPES: MOCKING HOMO HYPOCRITUS, 2007 ii EXOPLANET OBSERVING FOR AMATEURS THIRD EDITION Bruce L. Gary Reductionist Publications, d/b/a 5320 E. Calle Manzana Hereford, AZ 85615 iii Bruce L. Gary 5320 E. Calle Manzana Hereford, AZ 85615; SA [email protected] Cover Illustration: WASP-10 light curve, 2008 November 14, by the author, using a 14-inch Meade LX200 telescope and an SBIG ST-8XE CCD, unfiltered. The sketch is a scale- accurate depiction of exoplanet WASP-10b transiting in front of its parent star, WASP-10a. Copyright 2010 by Bruce L. Gary All rights reserved except for brief passages quoted in a review. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form and by any means: electronic, mechanical, photocopying, recording or otherwise without express prior permission from the publisher. Requests for usage permission or additional information should be addressed to: “Bruce L. Gary” <[email protected]> or Reductionist Publications, d/b/a 5320 E. Calle Manzana Hereford, AZ 85615 Second Edition (plus): 2010 October 22 (typo and other corrections) Second Edition: 2009 November 10 First edition: 2007 August Printed by Mira Digital Publishing, St. Louis, MO ISBN 978-0-9798446-3-8 iv v Dedicated to the memory of Carl Sagan A giant among men, who would have loved the excitement of exoplanet discoveries, which would have further inspired him to speculate about life in the universe. vi Author’s amateur exoplanet light curve of WASP-10 made November 14, 2008 with a 14-inch Meade LX200 telescope and no filter. Exoplanet WASP-10b moves in front of the star during contact 1 to 2, is obscuring ~3.6 % of the star’s disk between contacts 2 and 3, and is moving off the star during contacts 3 to 4. The smooth variation between contact 2 and 3 is produced by stellar “limb darkening.” The lower plot is the differences between individual measurements (one per image) and a simple model, showing that systematic variations are too small to notice, implying that the model fit is an adequate representation of the measurements for the purpose of inferring mid-transit time, transit length and transit shape. WASP-10 is similar in brightness (V-mag = 12.7) to other exoplanet stars (V-mag = 11.2) and is slightly redder than most (B-V ~ 1.1 versus 0.63). vii C O N T E N T S Preface to Second Edition 1 Preface to First Edition 3 Introduction 7 1 Could I Do That? 10 2 Observatory Tour 17 3 Exoplanet Projects 23 4 BTE List 28 5 Planning the Night 33 6 Atmosphere Tutorial 40 7 Filter Choice 48 8 Flat Fields 56 9 Dark Frames 64 10 Exposure Times and Defocusing 65 11 Focus Drift 71 12 Autoguiding 76 13 Photometry Aperture Size 78 14 Photometry Pitfalls 83 15 Image Processing 86 16 Three Photometry Methods Previewed 91 17 Spreadsheet Processing - Comp/Chk and Ensemble 96 18 Spreadsheet Processing - Artificial Star 106 19 Star Colors 117 20 Stochastic SE Budget 126 viii 21 Exoplanet Stars are Not Variable Stars 137 22 Archiving Amateur Data and Searching for Anomalies 144 23 The Optimum Observatory 149 24 The Joy of Exoplanet Observing 152 Appendix A – Flat Field Evaluation 155 Appendix B – Selecting Target from Candidate List 163 Appendix C – Air Mass from JD 166 Appendix D - Planet Size Model 167 Appendix E – Measuring CCD Linearity 188 Appendix F – Measuring CCD Gain 198 Appendix G – Plotting Light Curve Data 200 Appendix H – Comparing Filters 202 Appendix I – Transit Model and Fitting Procedure 213 Appendix J – Amateur Spectroscopy 220 Abbreviations 221 Glossary 225 Astronomy Hardware Company Contact Info 234 Acknowledgements 237 References 238 Index 240 ix ───────────────────────────────── PREFACE To Second Edition ───────────────────────────────── Two years ago I wrote the First Edition of this book. At that time there were 15 Bright Transiting Exoplanets, BTEs; now there are 46. At the same time that I published the First Edition I began a web-based archive for amateur observations submitted to me, called the Amateur Exoplanet Archive, AXA. After the first year the AXA contained 178 amateur-submitted light curves; today it has 666. A lot has happened in the last two years. Even though I’m using the same hardware and software now, my image processing and data analysis of image readings is considerably improved. This has been another surprise to me after I began writing the Second Edition. Most of the advice I offered in the First Edition is still basically valid, but it is not optimum. Several changes in observing strategy and data analysis are presented in this edition. For example, I used to recommend an R-band filter; now I recommend observing with a “clear with blue-blocking” filter (i.e., CBB-band). Even a clear filter (or no filter) is usually better than using an R-band filter, assuming your telescope aperture isn’t greater than about 16 inches. Another example, something that never occurred to me until other amateurs reported good results with it, is the strategy of “defocusing” when observing bright stars (e.g., V-mag < 10). I have seen the benefits of defocusing, to the point of producing donut shapes, for such stars. Occasionally an AAVSO observer wanting to observe exoplanet transits would ask why there weren’t any “comp stars” in the finder charts on the AXA web page devoted to each exoplanet. Since I made the transition from AAVSO observing to exoplanets a few years ago I understood the question, so I devote a chapter to explaining why having “comp” stars, with calibrated magnitudes, are not relevant for exoplanet observing. This Second Edition also describes the “big picture” for archiving amateur exoplanet data for use by professionals. A year ago I began collaboration with Caltech to transfer AXA data files and their transit fit solutions to Caltech’s IPAC computer for inclusion in the NStED archive (IPAC = Infrared Processing and Analysis Center; NStED = NASA/IPAC/NExSci Star and Exoplanet Database). This is where the professionals go to see what’s available in the public domain about their favorite exoplanet system. Having amateur data at the same site, and in the same data download format, is an important step in bridging the professional/amateur divide in a way that benefits both groups. In the past year the Czech Astronomical Society has created an archive for amateur data submissions, called the Exoplanet Transit Database, ETD. My two year old AXA has become so “successful” that I can’t keep up with data submissions if I continued to update plots of transit properties (such as mid-transit time versus date, transit length versus date, etc). I have therefore discontinued routine updates of the plots, which has given me free time for observing, and I look forward to the ETD taking over AXA’s role. These new developments are described in the Second Edition. Another change in this edition is a slightly larger page size. This means figures can be wider and therefore presented in higher quality. An expensive improvement is the use of a color printer for all pages; this means it’s not necessary to search through a central insert section to see what a figure looks like in color, which was necessary in the First Edition. 1 PREFACE – Second Edition The activity level of amateurs in observing exoplanets has grown pretty much as I expected two years ago. The AXA, for example, has 48 regular contributors. Interestingly, only six of these are in the United States; 41 are in Europe. None are in California or Arizona, which are two very active places for AAVSO observing. Exoplanets seem to have a greater appeal in Europe, which still puzzles me. However, I predict that amateurs in California, Arizona and other USA states, plus the Chinese, Indians, Japanese, will join the ranks of avid amateur observers of exoplanet transits in due time. The First Edition was printed and sold at cost until I ran out of copies. A PDF-document version of the book was available at a web site for free downloads. During the first two months approximately 2000 downloads were logged. This high number of downloads still puzzles me, since there aren’t that many amateurs observing exoplanets. The free PDF of the First Edition will remain available, at http://brucegary.net/book_EOA/x.htm. This Second Edition was for exclusive sale by Adirondack Astronomy until that company went out of business (summer of 2010). A few copies of the Second Edition are for sale by Starizona, one of the finest astronomy stores in America (starizona.com/acb/). A free PDF download of the Second Edition (Plus) is available at brucegary.net/book_EOA/x.htm. 2 ───────────────────────────────── PREFACE To First Edition (Updated) ───────────────────────────────── The search for planets orbiting other stars is interesting to even my daughters and neighbors. Why the public fascination with this subject? I think it’s related to the desire to find out if we humans are “alone in the universe.” This would explain the heightened interest in exoplanet searchers to find Earth-like planets. NASA and the NSF are keenly aware of this, and they are currently formulating a “vision” for future funding that is aimed at Earth-like exoplanet discoveries.