EDP Sciences
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Volume 373, Number 1, July I 2001
Page(s) 222 - 235
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20010610

A&A 373, 222-235 (2001)
DOI: 10.1051/0004-6361:20010610

NLTE accretion disc models for the AM Canum Venaticorum systems

M. R. Nasser1, J.-E. Solheim1 and D. A. Semionoff2

1  University of Tromsø, Department of Physics, 9037 Tromsø, Norway
2  Institute of Theoretical Physics and Astronomy, A. Gostauto 12, Vilnus 2600, Lithuania

(Received 30 January 2001 / Accepted 10 April 2001 )

We present models of the optical spectra of two types of accretion disc atmospheres: a pure helium model and a H-He model, in a low mass ratio, helium transferring, interacting binary white dwarf system. The computations are restricted to stationary discs in LTE and NLTE cases. We also investigate the influence on the spectra of some of the disc parameters such as the mass accretion rate, the angle of inclination, the H/He mass ratio, and the inner and outer radius of the disc. Departures from LTE are also investigated in order to assess the necessity of computing more complicated and more time consuming models. We found that differences in predicted equivalent widths of helium line computed in LTE and NLTE models range between 10 and 40 percent. Finally we compare our disc models with 4 of the AM CVn systems observed with the Nordic Optical Telescope: AM CVn, HP Lib, V803 Cen and CR Boo to determine their parameters as mass transfer rates and inclinations of their discs.

Key words: stars: novae, cataclysmic variables -- accretion discs -- individual: AM CVn, HP Lib, V803 Cen, CR Boo

Offprint request: M. R. Nasser, M.R Nasser@phys.uit.no

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