HS 0146+1847 – a DAZB white dwarf of very unusual composition

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 Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁵ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

Received: 14 March 2005
Accepted: 22 April 2005

Abstract

HS 0146+1847, originally identified as a white dwarf candidate in proper motion surveys, was rediscovered as a candidate in the Hamburg Quasar Survey. Spectra obtained for the SPY (ESO Supernova Ia Progenitor) survey show strong Balmer and Ca II lines, suggesting a classification as DAZ white dwarf. Contrary to the objects known so far in this class, HS 0146+1847 has a helium-rich atmosphere at  = 11 500 K. This is confirmed by very weak He lines, changing the classification to DAZB. Mg and Fe lines are also detected. We discuss the physics of Balmer line broadening by neutral helium, present a spectral analysis and note some implications for the accretion/diffusion scenario of heavy elements in cool white dwarfs.