|Annu. Rev. Astron. Astrophys. 1999. 37:
Copyright © 1999 by . All rights reserved
Ultraviolet observations have opened a new, and unexpectedly rich, window on old stellar populations that has revealed phenomena that are either difficult or impossible to study at longer wavelengths. The identification of the UVX component with low-mass, small-envelope stars has led to the recognition that the spectra of distant E galaxies are remarkably sensitive to what in traditional stellar population research would have been regarded as subtle astrophysical processes, including giant-branch mass loss, helium enrichment, and atmospheric diffusion. The fact that these processes are manifestly not properly understood at the moment, precluding a definitive interpretation of the UVX in terms of global population parameters, is less important than the long-term promise of UV observations as powerful probes of galaxy evolution.
Acknowledgments : For comments, figures, and other help in preparing this paper, I am most grateful to Ralph Bohlin, Tom Brown, Dave Burstein, Daniela Calzetti, Jeff Crane, Ben Dorman, Harry Ferguson, Ian Freedman, Richard de Grijs, Wayne Landsman, Ray Ohl, Alvio Renzini, Bob Rood, Ted Stecher, and Sukyoung Yi. This work has been supported in part by NASA Long Term Space Astrophysics grant NAG5-6403.