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Issue A&A Volume 385, Number 3, April III 2002 Page(s) 995 - 1007 Section Stellar atmospheres DOI 10.1051/0004-6361:20020194

A&A 385, 995-1007 (2002)
DOI: 10.1051/0004-6361:20020194

Element abundances in cool white dwarfs

II. Ultraviolet observations of DZ white dwarfs

B. Wolff¹, D. Koester¹ and J. Liebert<sup>2

1</sup>  Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany
    e-mail: koester@astrophysik.uni-kiel.de
²  Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
    e-mail: liebert@as.arizona.edu

(Received 21 December 2001 / Accepted 31 January 2002 )

Abstract
We present a small data base of homogeneously derived photospheric element abundances of DZ white dwarfs and related objects. Our previous investigations are supplemented with the analysis of ultraviolet spectra for nine white dwarfs. Of particular interest is the detection of L absorption in van Maanen 2 and a determination of the effective temperature of this star. The new value is about 1000 K lower than previous results due to the strong ultraviolet absorption by metals which has to be considered consistently. The metal abundances of our sample stars are compatible with the predictions from the two-phase accretion model of Dupuis et al. (1992, 1993a, 1993b). Small deviations can be observed for the abundance ratios in some objects. This could indicate non-solar metal-to-metal ratios in the accreted material. Hydrogen can be detected in virtually all of our objects. However, its average accretion rate must be at least two orders of magnitude lower than the metal accretion rate.

Key words: stars: abundances -- stars: atmospheres -- white dwarfs -- ultraviolet: stars

Offprint request: B. Wolff, wolf@astrophysik.uni-kiel.de

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