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Astron. Astrophys. 339, 518-524 (1998)

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Are the red dwarfs in cataclysmic variables main-sequence stars?

K. Beuermann 1, I. Baraffe 2, U. Kolb 3 and M. Weichhold 1

1 Universitäts-Sternwarte, Geismarlandstrasse 11, D-37083 Göttingen, Germany
2 C.R.A.L. (UMR 5574 CNRS), Ecole Normale Supérieure de Lyon, F-69364 Lyon Cedex 07, France
3 Astronomy Group, University of Leicester, University Road, Leicester LE1 7RH, UK

Received 19 June 1998 / Accepted 3 September 1998

Abstract

We show that the secondaries in short-period cataclysmic variables with orbital periods [FORMULA] hr are close to the solar-abundance main sequence defined by single field stars. In cataclysmic variables with [FORMULA] hr, the earliest spectral types at a given period correspond to main sequence stars, while the majority of secondaries have later spectral types. Possible causes are nuclear evolution prior to mass transfer and lack of thermal equilibrium due to mass transfer. A comparison with evolutionary sequences obtained with up-to-date stellar models implies unusually high transfer rates and a large fraction of systems with evolved donors. There is no evidence for a secondary of low metallicity in any of the well-studied cataclysmic variables.

Key words: stars: novae, cataclysmic variables - stars: low-mass, brown dwarfs – binaries: close – stars: abundances

Send offprint requests to: beuermann@uni-sw.gwdg.de

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© European Southern Observatory (ESO) 1998

Online publication: October 21, 1998
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