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A Binary Model for the UV-upturn of Elliptical Galaxies

Published online by Cambridge University Press:  01 December 2006

Z. Han ,
Ph. Podsiadlowski ,
A.E. Lynas-Gray  and
K. Schawinski
Z. Han
Affiliation:
National Astronomical Observatories/Yunnan Observatory, the Chinese Academy of Sciences, Kunming 650011, China email: zhanwenhan@hotmail.com
Ph. Podsiadlowski
Affiliation:
University of Oxford, Department of Astrophysics, Keble Road, Oxford OX1 3RH
A.E. Lynas-Gray
Affiliation:
University of Oxford, Department of Astrophysics, Keble Road, Oxford OX1 3RH
K. Schawinski
Affiliation:
University of Oxford, Department of Astrophysics, Keble Road, Oxford OX1 3RH
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Abstract

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The discovery of an excess of light in the far-ultraviolet (UV) in 1969 in elliptical galaxies was a major surprise. While it is now clear that this UV excess (UV-upturn) is probably caused by an old population of helium-burning stars. Han et al. (2002, 2003) proposed a binary model for the formation of hot subdwarfs (helium burning stars) and the model can reproduce the observations in our Galaxy. By applying the binary model to the study of evolutionary population synthesis, we have obtained an a priori model for the UV-upturn of elliptical galaxies. The model shows that the UV-upturn is most likely resulted from binary interactions and it is universal (not very much metallicity-dependant) in ellipticals. This has major implications for understanding the evolution of the UV-upturn and elliptical galaxies in general; contrary to previous postulates, it implies that the UV-upturn is not a sign of age, but could be a potentially powerful indicator for a recent minor burst of star-forming activity.

Keywords

ultraviolet: galaxiesgalaxies: elliptical and lenticular, cDstars: binaries: close
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S241: Stellar Populations as Building Blocks of Galaxies , December 2006 , pp. 181 - 182
Copyright
Copyright © International Astronomical Union 2007

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