Metal traces in white dwarfs of the SPY (ESO Supernova Ia Progenitor Survey) sample^*

¹ Institut für Theoretische Physik und Astrophysik, University of Kiel, 24098 Kiel, Germany e-mail: koester@astrophysik.uni-kiel.de
² Dept. of Physics & Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
³ Dr.-Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstr. 7, , Germany
⁴ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁵ Department of Physics and Astronomy, The University of Georgia, Athens, GA 30602-2451, USA

Received: 30 August 2004
Accepted: 5 November 2004

Abstract

We search for faint Ca II lines in the spectra of about 800 apparently single white dwarfs observed at high resolution for the SPY (ESO Supernova Progenitor Survey) survey. Photospheric Ca is detected in 24 DAZ; in 25 mostly hot objects the observed lines must be interstellar. We also rediscover 9 strong H and K lines in helium-dominated atmospheres and discover for the first time faint lines in 8 DB. Most of these also show faint hydrogen lines and are thus classified DBAZ. The distribution of metal abundances is discussed and compared with the predictions of the accretion/diffusion scenario. We argue that the observations are easier to understand in a scenario of continuous ongoing accretion with rates varying with the conditions of the ambient medium, rather than with the strongly idealized “two phase accretion/diffusion scenario” of [CITE] ([CITE], [CITE],b).