Issue |
A&A
Volume 419, Number 3, June I 2004
|
|
---|---|---|
Page(s) | 1057 - 1076 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20040085 | |
Published online | 07 May 2004 |
Detached white dwarf main-sequence star binaries
Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK e-mail: U.C.Kolb@open.ac.uk
Corresponding author: B. Willems, b-willems@northwestern.edu
Received:
17
July
2003
Accepted:
27
February
2004
We initiated a comprehensive state of the art binary
population synthesis study of white dwarf main-sequence star (WDMS)
binaries to serve as a foundation for subsequent studies on
pre-cataclysmic variables, double white dwarfs, and white dwarf +
B-star binaries. We considered seven distinct formation channels
subdivided into three main groups according to the evolutionary
process that gives rise to the formation of the white dwarf or its
helium-star progenitor: dynamically stable Roche-lobe overflow
(Algol-type evolution), dynamically unstable Roche-lobe overflow
(common-envelope evolution), or stellar winds (single star
evolution). For each formation channel, we examine the sensitivity
of the population to changes in the amount of mass lost from the
system during dynamically stable Roche-lobe overflow, the
common-envelope ejection efficiency, and the initial mass ratio or
initial secondary mass distribution. In the case of a flat initial
mass ratio distribution, the local space density of WDMS binaries is
of the order of ~. This number
decreases to ~
when the initial
mass ratio distribution is approximately proportional to the inverse
of the initial mass ratio. More than 75% of the WDMS binary
population originates from wide systems in which both components
essentially evolve as if they were single stars. The remaining part
of the population is dominated by systems in which the white dwarf
is formed in a common-envelope phase when the primary ascends the
first giant branch or the asymptotic giant branch. When dynamically
stable mass transfer proceeds highly conservative and the
common-envelope ejection process is very efficient, the birthrate of
WDMS binaries forming through a common-envelope phase is about 10
times larger than the birthrate of WDMS binaries forming through a
stable Roche-lobe overflow phase. The ratio of the number of helium
white dwarf systems to the number of carbon/oxygen or
oxygen/neon/magnesium white dwarf systems derived from large samples
of observed WDMS binaries by, e.g., future planet-search missions
such as SuperWASP, COROT, and Kepler may furthermore constrain the
common-envelope ejection efficiency.
Key words: stars: binaries: general / stars: evolution / stars: white dwarfs / methods: statistical
© ESO, 2004
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