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Astron. Astrophys. 349, L17-L20 (1999)


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Letter to the Editor

Stability and energetics of mass transfer in double white dwarfs

Zhanwen Han 1,2,3 and Ronald F. Webbink 4

1 Yunnan Observatory, Academia Sinica, Kunming, 650011, P.R. China
2 National Astronomical Observatories, Chinese Academy of Sciences
3 Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK (zhanwen_han@163.net or zhanwen@ast.cam.ac.uk)
4 Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801, USA (webbink@astro.uiuc.edu)

Received 15 July 1999 / Accepted 12 August 1999

Abstract

The donor star in an interacting double white dwarf lies deep within the potential well of the accretor, a condition which both alters the minimum mass transfer rate needed to generate an Eddington luminosity, and limits the fraction of matter which can be driven from the binary in a super-Eddington wind. That mass loss itself alters the threshold condition for the onset of dynamical instability of the donor star. We show that, unless the mass of the accreting star is extremely near the Chandrasekhar limit, a significant fraction (exceeding 0.5 for accretors of mass [FORMULA]) must be retained, even when the nominal accretion luminosity far exceeds the Eddington limit. In super-Eddington accretion, the accreted envelope almost certainly extends beyond the orbit of the donor, and will trigger white dwarf merger in a common envelope.

Key words: instabilities – stars: binaries: close – stars: white dwarfs

Send offprint requests to: Z. Han

© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999

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