Introduction

A favourite quotation by astronomers is a passage by the French philosopher, Auguste Comte (1798–1857). The nineteenth lesson of his Cours de Philosophie Positive appeared in 1835 and was one of several lessons dealing with the theory of knowledge in astronomy. With reference to the stars, he wrote:

A little later he continued: ‘I persist in the opinion that every notion of the true mean temperatures of the stars will necessarily always be concealed from us’ [1].

These passages may be amusing in the light of present knowledge, and it seems probable that Comte was ignorant of Fraunhofer's investigations from about 1814 to 1823 in which he described the absorption lines in solar and stellar spectra (see Sections 2.4 and 2.5).

Introduction

A miscellany of topics is covered in this final chapter. The first section discusses the spectra of a few individual peculiar stars of unusual interest, which appear not to be members of the broader groups of peculiar stars discussed under the headings of Chapter 9.1 A large number of stellar spectral idiosyncrasies could have been included here, but I have restricted the discussion to only a few objects. Several outstanding candidates were omitted, including β Lyrae (probably the star with the greatest number of spectroscopic references in the entire literature), because it has been referred to, albeit briefly, in earlier chapters; and also the spectroscopic binary and supergiant ζ Aurigae, with its atmospheric eclipses.

Secondly, two major topics of importance are treated which fell outside the headings in earlier chapters. The Wilson–Bappu effect encompasses the calcium emission lines from the chromospheres, or hot turbulent outer layers, of the cooler stars. The analysis of these lines has become a major method of determining stellar luminosities and distances.

In addition, the topic of interstellar absorption lines in stellar spectra is reviewed. This is an appropriate topic for a book on stellar spectroscopy, as it is the analysis of the starlight that reveals the presence of interstellar clouds along the line of sight to the star. Moreover, this subject played a big role in the advent of far ultraviolet spectroscopy from above the atmosphere.

The first edition of this book was published more than a quarter century ago, and at the time of writing this it has long been out of print and is also out of date.

In 2007 I decided to up-date it with this second edition. The main purpose was to bring the story of stellar spectroscopy forwards from about 1970, the closing date for material in the first edition, to about 2000. A secondary aim was to correct a number of typographical and factual errors that had crept into the first edition. The first edition manuscript was mainly handwritten and typed by a secretary prior to submission in the days before computers were widespread for text formatting. On the other hand, this second edition was prepared using LaTeX which has (I hope) permitted amuch lower error rate. I entered the entire manuscript at a keyboard myself, so I am solely responsible if any typographical errors remain.

Since 1970 there has been a huge advance in all fields of astronomy, especially in stellar astrophysics and spectroscopy. In fact, about as many papers on stellar spectroscopy have been published in the research literature in the last three decades of the twentieth century as in all the time before 1970. During these last few decades since the publication of the first edition, many discoveries were made using stellar spectroscopy, and there were also important instrumental advances in spectrograph design.

My main motivation for writing this book was an act of selfindulgence. As a hobby I enjoyed delving into the earlier literature of astronomical spectroscopy. As a practising observational astronomer, I found it especially refreshing to have a feel for the way the topic had developed, and to be able to glimpse at the lives of some of the early pioneers in stellar spectroscopy.

My hobby began in 1974 when I was at the Observatoire de Paris-Meudon on a fellowship. I frequently browsed in the excellent library there, and one day I began reading the collected papers of the eminent English astronomer Sir William Huggins, one of the founders of stellar spectroscopy. Huggins’ lucid and eloquent papers and his many remarkable achievements provided the inspiration from which my interest developed further, to form the basis for this book.

However, I had little time to pursue these interests very intensively until 1981, when an opportunity arose that allowed me to spend a year in Germany with the support of the Alexander von Humboldt Foundation, while on sabbatical from the University of Canterbury. I went to the Landessternwarte (State Observatory) in Heidelberg and resolved to spend most of my time there researching and writing a book on the development of stellar spectroscopy.

This book is not primarily intended for the science historian, nor is it a popular book for the layman, although I hope that readers in both these categories may find material here which is useful or interesting.