A&A 365, 491-507 (2001)
DOI: 10.1051/0004-6361:20000147
Population synthesis for double white dwarfs
I. Close detached systems
G. Nelemans1, L. R. Yungelson1, 2, S. F. Portegies Zwart3 and F. Verbunt41 Astronomical Institute "Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 Institute of Astronomy of the Russian Academy of Sciences, 48 Pyatnitskaya Str., 109017 Moscow, Russia
3 Department of Physics and Center for Space Research, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
4 Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
(Received 3 July 2000 / Accepted 19 October 2000 )
Abstract
We model the population of double white dwarfs in the Galaxy and
find a better agreement with observations compared to earlier
studies, due to two modifications. The first is the treatment of the
first phase of unstable mass transfer and the second the modelling
of the cooling of the white dwarfs.
A satisfactory agreement with observations of the local sample of
white dwarfs is achieved if we assume that the initial binary
fraction is 
50% and that the lowest mass white dwarfs (
) cool faster than the most recently published cooling
models predict.
With this model we find a Galactic birth rate of close double
white dwarfs of 0.05 yr-1, a birth rate of AM CVn systems of
0.005 yr-1, a merger rate of pairs with a combined mass
exceeding the Chandrasekhar limit (which may be progenitors of
SNe Ia) of 0.003 yr-1 and a formation rate of planetary nebulae
of 1 yr-1. We estimate the total number of double white dwarfs
in the Galaxy as 2.5 108.
In an observable sample with a limiting magnitude
we predict the presence of 855 white dwarfs of which
220 are close pairs. Of these 10 are double CO white
dwarfs of which one has a combined mass exceeding the Chandrasekhar
limit and will merge within a Hubble time.
Key words: stars: white dwarfs -- stars: statistics -- binaries: close -- binaries: evolution
Offprint request: G. Nelemans SIMBAD Objects
© ESO 2001