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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
Received 19 June 1998 / Accepted 3 September 1998
We show that the secondaries in short-period cataclysmic variables with orbital periods hr are close to the solar-abundance main sequence defined by single field stars. In cataclysmic variables with 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
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Online publication: October 21, 1998