Introduction

The theory of stellar structure and evolution is one of the most exact of the astrophysical sciences. It is inextricably involved in many of the topics needed to understand the role which high energy astrophysical processes play in the origin and evolution of stars and galaxies, providing, for example, evidence on their chemical abundances, the ages of the systems, and so on. The objective of this chapter is to provide a succinct summary of a number of the key results needed in the subsequent development of the story. Many of the equations and concepts will recur in different guises in the course of the exposition. There are many excellent books on these vast topics, my personal favourites being the books by Tayler, Karttunen and his colleagues, and by Kippenhahn and Weigert (Tayler, 1994; Karttunen et al., 2007; Kippenhahn and Weigert, 1990). The last volume is a classic and is particularly strong on the physics of the stars.

Basic observations

It is necessary to become familiar with some of the vocabulary of the study of the stars and the basic results of observation. These studies begin with measurements of the total amount of radiation emitted by a star, its luminosity L, and its surface temperature T. The spectra of stars are not black-bodies and so the effective temperature Teff is introduced. It is defined to be the temperature of a black-body of the same radius as the star which would emit the same luminosity.