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[42.02] Dwarfs on a Low-Carbon Diet: Modelling the Chemically Peculiar Secondaries of CVs

D. Homeier (U. Georgia), T. E. Harrison (NMSU), T. S. Barman (Wichita State U.), S. B. Howell (NOAO)

Secondary stars of cataclysmic variables show a variety of abundance anomalies that might be caused by deposition of CNO-processed material. We have calculated PHOENIX stellar atmosphere models for late-type stellar and substellar companions using chemical equilibrium compositions for a range of carbon-depleted and/or oxygen-enriched elemental abundances. We present comparisons of our models with medium-resolution IR spectra of CV secondaries, including the possibly substellar secondary of the EF Eridani system. LTE models of the K-band spectrum are consistent with a T_eff in the brown dwarf range and show that the complete lack of CH₄ and CO absorption features in this object requires a [C/Fe] ratio more than 2 dex below the solar value. We compare our models to temperature estimates from light curve analyses and present a first irradiated model of the secondary, that takes into account the effect of the impinging flux from the white dwarf primary. This project has been supported by grants from the National Science Foundation and the NASA NStars program.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.