Introduction

The successful analysis of the absorption lines in stellar spectra to obtain the abundances of the different elements became a feasibility for stars of a range of spectral types from the early 1940s. In this chapter the development of the subject from about 1940 to the end of the twentieth century is reviewed. In addition, the developments in stellar atmosphere theory, in instrumental techniques and in laboratory data which made abundance analyses possible are discussed here, from the position reached at the end of Chapter 7.

Several important preliminary problems first had to be settled before substantial progress was possible. Those relating to instrumental techniques and laboratory data are deferred until Section 10.8, and we treat here the problems that arose in the theory which was necessary to interpret stellar spectra. First, the whole issue of stellar temperature measurements from the continuous spectra, or spectral flux gradients, was in a mess in the 1920s. This problem was gradually sorted out during the 1930s decade once it was realized that stars do not really radiate like black bodies. This is the subject of Section 10.2.

Secondly, for the analysis both of the flux gradients and of spectral lines, some sort of model was necessary to describe the structure of stellar atmospheres. The development of model atmospheres from McCrea's first work in 1931 is therefore vital to the overall discussion.