EXOPLANET OBSERVING FOR AMATEURS - brucegary.net

170 Pages·2007·3.72 MB·English

EXOPLANET OBSERVING
FOR AMATEURS
Books by Bruce L. Gary

ESSAYS FROM ANOTHER PARADIGM, 1992, 1993 (Abridged)

GENETIC ENSLAVEMENT:
A CALL TO ARMS FOR INDIVIDUAL LIBERATION, 2004, 2006

THE MAKING OF A MISANTHROPE: BOOK 1, 2005

A MISANTHROPE’S HOLIDAY: VIGNETTES AND STORIES, 2007

QUOTES FOR MISANTHROPES: MOCKING HOMO HYPOCRITUS, (2007)

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EXOPLANET OBSERVING
FOR AMATEURS

Bruce L. Gary

Reductionist Publications, d/b/a
5320 E. Calle Manzana
Hereford, AZ 85615

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Reductionist Publications, d/b/a
5320 E. Calle Manzana
Hereford, AZ 85615
USA

Copyright 2007 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
5320 E. Calle Manzana
Hereford, AZ 85615

First edition: 2007 August

Printed by Mira Digital Publishing, St. Louis, MO

ISBN 978-0-9798446-3-8

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Dedicated to the memory of

Carl Sagan
A giant among men, who would have loved the excitement of exoplanet
discoveries, that would have further inspired him to speculate about
life in the universe.

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Author’s amateur exoplanet light curve of XO-1 made in 2006 (average of two
transits) with a 14-inch telescope and R-band filter at his Hereford Arizona
Observatory. Exoplanet XO-1b moves in front of the star during contact 1 to contact
2, is obscuring ~2.2 % 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.”

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C O N T E N T S

Preface 1

Introduction 5

1 Could I Do That? 8

2 Observatory Tour 14

3 Exoplanet Choices 19

4 Planning the Night 27

5 Flat Fields 34

6 Dark Frames 42

7 Exposure Times 44

8 Focus Drift 48

9 Autoguiding 55

10 Photometry Aperture Size 57

11 Photometry Pitfalls 62

12 Image Processing 64

13 Spreadsheet Processing 67

14 Star Colors 75

15 Stochastic SE Budget 87

16 Anomalies: Timing and LC Shape 95

17 Optimum Observatory 99

Appendix A – Flat Field Evaluation 103

Appendix B – Selecting Target from Candidate List 112

Appendix C – Air Mass from JD 115

Appendix D - Planet Size Model 116

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Appendix E – Measuring CCD Linearity 138

Appendix F – Measuring CCD Gain 148

Glossary 150

References 159

Index 161

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─────────────────────────────────
PREFACE
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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.

The author’s favorite telescope, a Meade RCX400 14-inch on an equatorial wedge.

The public’s interest in planets beyond our solar system may also account for Sky and
Telescope magazine’s interest in publishing an article about the XO Project, a
professional/amateur collaboration that found a transiting exoplanet XO-1 (since then
two more discoveries have been announced by this project). The above picture, from
the Sky and Telescope article (September, 2006), helps make the point that amateur
telescopes are capable of providing follow-up observations of candidates provided by
professionals using wide-field survey cameras. The XO Project is a model for future
professional/amateur collaborations.

Astronomers, ironically, have traditionally tried to remain aloof from things that
excited the general public. I recall JPL cafeteria conversations in the 1970s where I
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PREFACE
defended Carl Sagan’s right to communicate his enthusiastic love for astronomy to
the public. There was a “pecking order” in astronomy at that time, which may still
exist to some extent, in which the farther out your field of study the higher your
status. Thus, cosmologists garnered the highest regard, and those who studied objects
in our solar system were viewed with the least regard. My studies were of the moon,
but I didn’t care where I was in this hierarchy. At that time there was only one level
lower than mine: those who speculated about other worlds and the possibilities for
intelligent life on them.

How things change! We now know that planets are everywhere in the galaxy.
Billions upon billions of planets must exist! This is the message from the tally of 248
extra-solar planetary systems (as of mid-2007). Among them are 22 exoplanets that
transit in front of their star (15 that are brighter than 13th magnitude), and the number
is growing so fast that by the time this book appears the number could be two or
three dozen.

It is important to realize that bright transiting exoplanets are far more valuable than
faint or non-transiting ones! The bright transits allow for an accurate measure of the
planet’s size, and therefore density; and spectroscopic investigations of atmospheric
composition are also possible (successful in two cases). Even studies of the
exoplanet’s atmospheric temperature are open for investigation. When 2007 began,
only 9 bright transiting exoplanets were known. Six months later there were 14!

Few people realize that part of the explosion of known transiting exoplanets can be
attributed to the role played by amateur astronomers. Three of the 15 bright transiting
exoplanets were discovered by the XO Project, which includes a team of amateurs.
During the past few decades, when professional observatories have become more
sophisticated and plentiful, it is ironic that amateurs have kept pace, thanks to
improvements in technology that’s within amateur budgets, and we amateurs
continue to make useful contributions. The discovery of exoplanet is one of the most
fruitful examples!

Not only are amateurs capable of helping in the discovery of exoplanets through
collaborations with professionals, but amateurs are well-positioned to contribute to
the discovery of Earth-like exoplanets! This is explained in Chapter 16.

How can this be? After all, the professionals have expensive observatories at
mountain tops, and they use very sophisticated and sensitive CCD cameras. But with
this sophistication comes expensive operation on a per minute basis! With telescope
time so expensive, these highly capable facilities can’t be used for lengthy searches.
Moreover, big telescopes have such a small field-of-view (FOV) that there usually
aren’t any nearby bright stars within an image for use as a “reference.” The optimum
size telescope for most ground-based exoplanet discovery has an aperture between 20
and 40 inches, as explained in Chapter 17. Such telescopes are within the reach of
many amateurs. So far, most exoplanet discovery contributions by amateurs have
been with telescope apertures in the 10 to 14 inches size range. Thousands of these
telescopes are in use by amateurs today.
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