Koester, Detlev, 1941-, Girven, Jonathan, Gänsicke, B. T. (Boris T.) and Dufour, P.. (2011) Cool DZ white dwarfs in the SDSS. Astronomy & Astrophysics, Vol.530 . A114. ISSN 0004-6361

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Abstract

Aims. We report the identification of 26 cool DZ white dwarfs that lie across and below the main sequence in the Sloan Digital Sky Survey (SDSS) (u − g) vs. (g − r) two-color diagram; 21 of these stars are new discoveries. Methods. The sample was identified by visual inspection of all spectra of objects that fall below the main sequence in the two-color diagram, as well as by an automated search for characteristic spectral features over a large area in color space that included the main sequence. The spectra and photometry provided by the SDSS project are interpreted with model atmospheres, including all relevant metals. Effective temperatures and element abundances are determined, while the surface gravity has to be assumed and was fixed at the canonical value of logg = 8. Results. These stars represent the extension of the well-known DZ sequence towards cooler temperatures and fill the gap around Teff = 6500 K present in a previous study. The metal abundances are similar to those in the hotter DZ, but the lowest abundances are missing, probably because of our selection procedures. The interpretation is complicated in terms of the accretion/diffusion scenario, because we do not know if accretion is still occurring or has ended long ago. Independent of that uncertainty, the masses of the metals currently present in the convection zones – and thus an absolute lower limit of the total accreted masses – of these stars are similar to the largest asteroids in our solar system.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	White dwarf stars, Accretion (Astrophysics), Cosmic abundances, Diffusion
Journal or Publication Title:	Astronomy & Astrophysics
Publisher:	EDP Sciences
ISSN:	0004-6361
Date:	June 2011
Volume:	Vol.530
Page Range:	A114
Identification Number:	10.1051/0004-6361/201116816
Status:	Peer Reviewed
Publication Status:	Published
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URI:	http://wrap.warwick.ac.uk/id/eprint/39761

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