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Issue A&A
Volume 422, Number 1, July IV 2004
Page(s) 217 - 223
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20040248



A&A 422, 217-223 (2004)
DOI: 10.1051/0004-6361:20040248

Models for extremely metal-poor halo stars

A. Weiss1, H. Schlattl1, 2, M. Salaris2 and S. Cassisi3

1  Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Federal Republic of Germany
2  Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK
3  INAF - Osservatorio Astronomico Collurania, via Mentore Maggini, 64100 Teramo, Italy

(Received 11 February 2004 / Accepted 2 April 2004 )

Abstract
Two alternative scenarios concerning the origin and evolution of extremely metal-poor halo stars are investigated. The first one assumes that the stars have been completely metal-free initially and produced observed carbon and nitrogen overabundances during the peculiar core helium flash typical of low-mass Population III stars. The second scenario assumes that the initial composition resulted from a mixture of primordial material with ejecta from a single primordial supernova. Both scenarios are shown to have problems in reproducing C, N, and O abundances simultaneously, and both disagree with observed $^{12}{\rm C}/^{13}{\rm C}$-ratios, although in different directions. We concentrate on the most iron-poor, carbon-rich object of this class, HE 0107-5240, and conclude that the second scenario presently offers the more promising approach to understand these objects, in particular because evolutionary tracks match observations very well.


Key words: stars: low mass, brown dwarfs -- stars: interiors -- stars: abundances -- stars: evolution -- stars: individual: HE 0107-5240

Offprint request: A. Weiss, weiss@mpa-garching.mpg.de

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© ESO 2004


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