Reviews of `Cataclysmic Variable Stars: how and why they vary'

American Association of Variable Star Observers, in Newsletter, November 2001, by Aaron Price

"Cataclysmic Variable Stars: How and Why They Vary" by Coel Hellier is one of those rare books that successfully toes the line between being a scientific and a popular book. This book is so popular with HQ staff that it frequently is taken home and has to be tracked down when someone needs it! It works as both a reference and a straight-through read. As a reference, one can confidentally refer to it when coming across any type of unfamiliar CV. As a straight-through read, it is clearly structured and written in a lively style that makes it easy to go from start to finish.

The majority of the book is broken up into sections about the different types of CVs. Each section is well illustrated with light curves (many coming from AAVSO observations from observers like you), historical background, a breakdown of the system with easy-to-read diagrams, theory, and more. When mathematics is introduced it is always in a sidebar or appendix which allows those interested to get involved but does not require an understanding of the equations for those who wish to avoid math.

The book is not simply an encyclopedia of CVs, though. It covers everything from basic visual and CCD observing techniques to how to derive a stellar mass from your observations.

This is a book that every CV lover should own along with anyone who is interested in learning more about these enigmatic objects. The layout, illustrations, structure, and writing have all come together to create what is almost the perfect book on CVs. I hope the team that put together this book continues to work together on future endevours. If so, the future of variable star publications looks not variable at all, but bright and steady.

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Review in Observatory (June 2002; vol 122, p 181) by Robert Connon Smith

If you are a postdoc or experienced graduate student who wants a comprehensive account of everything that was known about cataclysmic variables (CVs) up to late 1994, then Brian Warner's book "Cataclysmic Varaibles" (CUP, 1995) is what you need. But it is so comprehensive that is is perhaps not the best introduction to the subject: something a bit more explanatory and less detailed may be what you are seeking. If so, look no further than the present book. The subtitle `How and why they vary' gives a clue to the emphasis and Coel Hellier has done a splendid job in presenting the essentials for understanding these enigmatic variable stars without burying the reader in detail.

Nonetheless, in thirteen short chapters and six appendices, he does include a remarkable amount of information in a clear and readable style which will be as accessible to amateur astronomers as to senior undergraduates or beginning graduate students. Such readers will appreciate the first chapter, which gives a very lucid overview of observing with small telescopes, both visually and with a CCD camera, with really practical advice: anyone who masters this chapter will have the confidence to start observing variable stars on their own.

Turning to CVs, Hellier first introduces the actors - the red and white dwarf companions, and the mass transfer the accounts for many of their bizarre properties - and the observed spectra before going on to discuss the long-term evolution of CVs. The short-term variability associated with outbursts and mass transfer is then introduced and forms the theme of much of the rest of the book. Beginning with outburst mechanisms, the treatment moves naturally on to super-outbursts, and the elliptical discs that are thought to account for the slightly non-synchronous super-humps that appear in the orbital light curves duing super-outburst. This leads on to siphons, winds, and streams, to magnetic CVs and to flickering and (quasi-periodic) oscillations. After a chapter on nova eruptions, the book ends with a discussion of variations on the secondary star (the red dwarf) and of various related types of variable with discs, winds and jets.

Although no deep mathematics appears, boxes in the test in many chapters, together with the first appendix, give a brief outline of most of the essential mathematics fro those who want it, and there are selected references to the original literature for those who want to explore the topic in more detail. The main text, however, is generally quite comprehensible without the boxed material or references. There appear to be rather few typos (on p.110, `Box 7.1' should be `Box 8.1'; Fig.9.11 doesn't appear to be cited in the text), but there are a few places where brevity or oversight has led to misleading statements. For example, in the footnote on p.3, minutes and seconds of right ascension are confusingly referred to as being `minutes and seconds of arc (right ascension)'; on line 3 of p.16, stability is confused with equilibrium (the line should say that a star is only in equilibrium if ...'); on p.107 the words `disc flare' suggest a time-dependent event rather than the `flared disc' under discussion. In the mathematical box on p.48, the treatment of the binary's response to mass transfer is misleading because it fails to include the response of the mass-losing star.

However, these are very minor criticisms of an excellent book which deserves to be much used (and, at this price, bought!).

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Review in the Journal of the British Astronomical Association (December 2001, vol 111, p350) by Gary Poyner

If you had asked a serious observer of cataclysmic variables (CVs) twelve months ago which book they regarded as the most important in their library, he or she would have said `Brian Warner's Cataclysmic Variable Stars' (Cambridge University Press, 1995), and they would have been correct. Those sentiments may well change after the arrival of this book. Coel Hellier has produced a book which is sure to become a classic within the amateur CV community for many years to come, and an excellent reference source for those pursuing the subject of CVs at undergraduate level.

In the first chapter the author introduces the reader to the basics of observing CVs both visually and with a CCD camera. There is enough information included to be useful to the absolute novice, and the more experienced observer (both visual and CCD) may well pick up a useful tip or two. But the nitty-gritty of the book begins with chapter two. Here we are introduced to the binary star system which constitutes a CV. The chapters progress through the orbital cycle, spectral characteristics of the system, evolution and discs, and outbursts. Elliptical discs and superoutbursts of the UGSU stars are well covered. Both magnetic and non-magnetic systems are dealt with in detail, as is the phenomenon of `flickering', something that nearly all CV observers have suspected, but have never really been too sure of.

The book concludes with chapters on novae, variations in the secondary star, X-ray binaries and six appendices, which includes a list of the CVs discussed in the book, as well as a list of variable star organisations, a description of variable star nomenclature, time conventions, notes on units and symbols and a mathematical description for deriving stellar masses. An excellent collection of computer-generated graphical diagrams adequately illustrates the main points made in the text.

It is not possible to write a detailed book on this subject without including mathematical formulae and (to some at least) mind bending equations, and this is no exception. However the main body of the text has been written in a non-mathematical way, with all the `heavy' physical equations and in depth descriptions being reserved for `boxes'. This means that the book can be read from cover to cover by someone who has little or no mathematical background, without the feeling that most of what has been written has passed over the reader's head. A real winner from the author.

I found myself disagreeing with Hellier on one point only, and that was concerning standstills in UGZ stars. The author states that `standstills always end with a decline to quiescence'. This is not the case. Standstills in several UGZ stars have been observed (by amateurs) to end in outburst. Although the physical processes behind these events are not yet fully understood, and are admittedly a fairly uncommon occurrence, the phenomenon is very real and easily detectable with backyard telescopes.

A big disappointment for me is that the author relies heavily on the AAVSO for the long term light curves included in the book. Although there is nothing intrinsically wrong with this (the AAVSO produces fine data) it might have been reasonable to expect a British astronomer, and one who has spoken to amateur groups in the UK in the past, to include some light curves from the BAAVSS. In fact not one BAAVSS light curve is included in the book, despite the Section possessing a massive database, which includes many CVs, whose data is readily available in electronic form. An excellent selection of CBA (Centre for Backyard Astrophysics) photometric light curves is however included.

Despite these minor points, Coel Hellier has come up with a classic book, written in a way that both serious student and casual CV observer can read, learn from and enjoy. Warner's aforementioned (and very expensive) book will still be the CV bible for those who wish to take a higher view of the subject, or for the many useful tables included within the text, but Hellier's Cataclysmic Variable Stars will reign supreme on the amateur CV observer's book shelf for many years to come.

If you are not yet a CV observer, then this fascinating book may well direct you to a field of study in which the amateur is making regular contributions (both visually and with CCDs) night after night, and adding to our understanding of these enigmatic objects. If you have already been bitten by the CV bug, then you simply must buy this book.

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Interacting Binaries Newsletter, No 6, March 2001

By Boris Gänsicke, Universitäts-Sternwarte, Göttingen, Germany.

``Cataclysmic Variable Stars: How and why they vary'' by Coel Hellier provides a good overview of the present state of CV research -- including some of the unresolved problems -- somewhat weighted from the point of view of an observer. The topic of CVs is embedded between an introduction to CCD photometry of variable stars and a short overview of related systems, such as X-ray binaries, AGN and YSOs. A large amount of well-prepared figures supports the text. Each chapter is supplemented with a number of ``boxes'' that give additional details about observation techniques, essential equations, or analysis methods.

The book addresses an incredible number of aspects. In fact, I found that almost every keyword coming to my mind in the context of CV reasearch is mentioned. This breadth is of course paid by a lack of depth -- the entire text is kept on 200 pages. As a consequence, penetrating some of the involved physics might at times be difficult for a young researcher. A more extended bibliography, especially pointing to a larger number of relevant non-CV papers, would have helped to prevent this shortcoming.

Summing up, ``Cataclysmic Variable Stars: How and why they vary'' is a crash course in CV research that brings the unfamiliar reader into the field within the shortest time, and prepares him/her for the more comprehensive overviews, such as Warner's book, or Frank, King & Raine's text on the theoretical aspects of accretion.

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Date: Thu, 1 Mar 2001
From: Joe Patterson (Columbia University)
To: news@cba.phys.columbia.edu
Subject: The CBA sells its soul?

Dear CBAers,

Before anyone grumbles too much about advertising in this hallowed forum, I wanted to sing some praises to Hellier's book. This is what I've been hoping for all along, a CV book written for advanced amateurs and undergraduates and yet not shunning physics. Very digestible. Some of you already own Warner's 1995 opus on the subject; an amazing book, now called "Big Book" or "The Bible" by those of us in The Biz... but sort of like taking a drink at a fire hydrant.

I recommend Hellier's book very highly, in fact I just ordered 30 copies! (Oh, and I think he might say some warm fuzzy things about the CBA, too.)

joe

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Review by Fred Ringwald (California State University, Fresno) on Amazon.com, June 25, 2001

Thanks, Coel, this book has made my job of involving undergraduates in my research (on CVs, of course) much easier. It is suitable for amateurs, too, being self-contained with its chapter on CCD photometry. It's also nicely produced, and yet the price is quite reasonable...: I have no qualms with telling them to go out and buy their own copies, necessary since both my copies are already in the hands of students.

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Brief comments on the AAVSO discussion forum:

To: aavso-discussion May 2001, message 55
Subject: [AAVSO-DIS] CV book
From: "Mike Simonsen"
Date: Fri, 25 May 2001 15:20:27 -0400

I ordered mine from amazon.com and it took about six weeks to get here. It was worth the wait.

I've read Warner's book once, and then had to buy a dozen books to help me decipher it. Hellier put the mathematics in side boxes so you can actually just read the text and get the story. This makes it a lot more enjoyable read the first time through.

Two thumbs up.

Mike Simonsen



To: aavso-discussion May 2001, message 57.
Subject: Re: [AAVSO-DIS] CV book
From: Aaron Price
Date: Thu, 24 May 2001 20:59:49 -0400 (EDT)

>
> Has anyone seen the new book "Cataclysmic Variable Stars" by Coel Hellier?
>

I'll be writing a review for it in this fall's JAAVSO and I can say now that it will be glowing. The book manages the rare feat of towing the line between mathematics and theory. It explains the theory in a very clear and engaging tone and will offer the math for those who want it, but not in a way that requires that you learn it.