12 - Laboratory astrophysics: atomic spectroscopy

Summary

Introduction

A close relationship has always existed between the progress of atomic theory and laboratory research on the one hand, and the growth of astrophysics on the other. That such a relationship should exist is not in the least surprising. The vast agglomeration of atoms, molecules, ions, and electrons that comprise every star and every nebula may in fact be regarded as an enormous physical laboratory, where matter is subjected to the most unusual and the most varied of physical conditions. Atomic studies in the laboratory should therefore logically supplement those in stellar atmospheres, and vice versa.

Leo Goldberg, Thesis, Harvard University, 1938.

These words describe the enduring relationship between astronomy and atomic physics and, in particular, the wonderful unity of laboratory and astrophysical plasmas. In this chapter we will explore the laboratory part of this unity and will discuss the measurements of some parameters and processes which are important to astronomy and atomic physics.

The determination of chemical abundances and the calculation of model atmospheres for the Sun and stars have become increasingly sophisticated since the landmark work of Goldberg and colleagues. However, despite the impressive progress, calculations based on the best existing atomic data, chemical abundances, and model atmospheres do not reproduce the measured, high-resolution, ultraviolet, solar spectrum nor do they match the center-to-limb variations. When high-resolution, ultraviolet, solar spectra (see Fig. 12.1) are examined it is apparent that the complex of overlapping and nearby lines (‘line blanketing’) could be responsible for much of the discrepancy between observations and calculations.