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UV Bright Stars and Planetary Nebulae in Elliptical Galaxies

Published online by Cambridge University Press:  30 March 2016

Henry C. Ferguson
Henry C. Ferguson*
Affiliation:
Space Telescope Science Institute

Abstract

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Far UV observations and optical studies of planetary nebula luminosity functions (PNLFs) offer complementary views of the late phases of stellar evolution in elliptical galaxies and spiral galaxy bulges. UV spectroscopy reveals that the hot stellar population is composite, with a mix of temperatures that varies from galaxy to galaxy. This changing mix is most likely due to changes in the relative numbers of stars that channel through the Post-Asymptotic Giant Branch (PAGB), Post-Early-AGB (PEAGB) and Extreme Horizontal Branch (EHB) phases of evolution. EHB stars appear to dominate the integrated λ < 2000 Å flux from galaxies with the strongest far-UV emission, but are too faint to resolve individually in even the nearest galaxies. Far UV images of M31 and M32 reveal a population of hot stars that are much brighter, but do not account for the majority of the far-UV flux. The sources detected are most likely low-mass PAGB stars (0.55 < M/M⊙ < 0.59). In contrast, the PNLF probes the PAGB star mass function at values greater than ∼ 0.6 M⊙. For a given galaxy the relative numbers of stars in these different branches of evolution are determined by the age and chemical evolution of the galaxy and by the physics of mass loss on the red giant branch. We review current constraints on the mass function of hot evolved stars in elliptical galaxies, highlight a few puzzles, and outline where future observations might contribute.

Type
II. Joint Discussions
Information
Highlights of Astronomy , Volume 10: Highlights of Astronomy. As presented at the XXIInd General Assembly of the IAU, 1994 , 1995 , pp. 493 - 497
Copyright
Copyright © Kluwer 1995

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