Letter to the Editor
Identification of 13 DB + dM and 2 DC + dM binaries from the Sloan Digital Sky Survey
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: firstname.lastname@example.org
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
© ESO, 2005