Accretion in the detached post-common-envelope binary LTT 560 (C. Tappert et al.)

Vol. 532In section 7. Stellar structure and evolution

Accretion in the detached post-common-envelope binary LTT 560

by C. Tappert, B. T. Gänsicke, L. Schmidtobreick, and T. Ribeiro, A&A 532, A129

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The paper presents the results of a high-resolution (70000) study of the post-common envelope close binary LTT 7987. A period of 3.5 hours, combined with the radial velocity variations obtained for both components, gives a mass ratio M_MS/M_WD = 0.31 and confirmed gravitational redshift of 19 km/s. Combined, the most likely WD mass is between 0.44 and 0.46 M_sun, depending on composition, and a companion mass of 0.14 to 0.15 M_sun, indicating that the main sequence star is fully convective. The system does not eclipse, and the main sequence star appears to be tidally distorted although not yet in contact with its Roche surface. Based on the derived metal abundances and the relatively short diffusion times of around 10^4 yrs, the authors conclude that the WD accretes at a rate of about 5x10^{-13}M_sun/yr. This will, according to the evolutionary scenario developed by the authors, increase as the companion approaches the Roche surface in about 3.5 Gyr owing to gravitational wave-induced angular momentum loss. It represents a pre-SU Uma system (nonmagnetic white dwarf cataclysmic system).