EDP Sciences
Free access
Volume 434, Number 3, May II 2005
Page(s) L13 - L16
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200500102

A&A 434, L13-L16 (2005)
DOI: 10.1051/0004-6361:200500102


Identification of 13 DB + dM and 2 DC + dM binaries from the Sloan Digital Sky Survey

E. J. M. van den Besselaar1, G. H. A. Roelofs1, G. A. Nelemans1, T. Augusteijn2 and P. J. Groot1

1  Department of Astrophysics, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
    e-mail: [besselaar;gijsroel;nelemans;pgroot]@astro.ru.nl
2  Nordic Optical Telescope, Apartado 474, Santa Cruz de La Palma, Spain
    e-mail: tau@not.iac.es

(Received 5 January 2005 / Accepted 22 March 2005)

We present the identification of 13 DB + dM binaries and 2 DC + dM binaries from the Sloan Digital Sky Survey (SDSS). Before the SDSS only 2 DB + dM binaries and 1 DC + dM binary were known. At least three, possibly 8, of the new DB + dM binaries seem to have white dwarf temperatures well above 30 000 K which would place them in the so called DB-gap. Finding these DB white dwarfs in binaries may suggest that they have formed through a different evolutionary channel than the ones in which DA white dwarfs transform into DB white dwarfs due to convection in the upper layers.

Key words: binaries: spectroscopic -- white dwarfs -- stars: late-type -- stars: evolution

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