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Astron. Astrophys. 358, 154-168 (2000)

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Accretion disc models for AM Canum Venaticorum systems

W. El-Khoury and D. Wickramasinghe

Astrophysical Theory Centre, Department of Mathematics, Australian National University; ACT 0200, Australia, (walid,dayal@maths.anu.edu.au)

Received 16 November 1999 / Accepted 16 March 2000

Abstract

Using a model of the vertical structure of accretion discs, we calculate disc spectra across a range of system parameters for the helium-rich AM CVn cataclysmic variables, and investigate thermal instabilities in their discs.

Applying a [FORMULA]-minimisation technique, predicted HeI and HI continuum and line profiles are compared with those observed for two such systems, AM CVn and CR Boo, to estimate several system parameters. We find:

  • mean accretor masses close to, but somewhat higher than, the [FORMULA] range predicted by present population synthesis studies;

  • typical helium-to-hydrogen number density ratios of [FORMULA], consistent with a helium-degenerate donor surrounded by a helium-rich envelope; and

  • mass-transfer rates of about [FORMULA], which may place the systems in the region of potential disc instability.

S-curves calculated for the best-fit models are consistent with a thermally-stable disc in AM CVn, and a thermally unstable disc in CR Boo.

Key words: stars: individual: AM CVn, CR Boo – stars: novae, cataclysmic variables – stars: evolution – stars: binaries: general

Send offprint requests to: W. El-Khoury

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© European Southern Observatory (ESO) 2000

Online publication: June 26, 2000
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