Annu. Rev. Astron. Astrophys. 1999. 37: 603-648
Copyright © 1999 by . All rights reserved

Reprinted with kind permission from , 4139 El Camino Way, Palo Alto, California, USA

For a PDF version of the article, click here.
For a Postscript version of the article, click here.

FAR-ULTRAVIOLET RADIATION FROM ELLIPTICAL GALAXIES

Robert W. O'Connell

Astronomy Department, University of Virginia, P.O. Box 3818, Charlottesville, Virginia 22903-0818

Abstract. Far-ultraviolet radiation is a ubiquitous, if unanticipated, phenomenon in elliptical galaxies and early-type spiral bulges. It is the most variable photometric feature associated with old stellar populations. Recent observational and theoretical evidence shows that it is produced mainly by low-mass, small-envelope, helium-burning stars in extreme horizontal branch and subsequent phases of evolution. These are probably descendants of the dominant, metal rich population of the galaxies. Their lifetime UV outputs are remarkably sensitive to their physical properties and hence to the age and the helium and metal abundances of their parents. UV spectra are therefore exceptionally promising diagnostics of old stellar populations, although their calibration requires a much improved understanding of giant branch mass loss, helium enrichment, and atmospheric diffusion.

Keywords: stellar populations, hot stars, mass loss, galaxy evolution

Table of Contents