Analysis of IUE spectra of helium-rich white dwarf stars

¹ Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-900 Porto-Alegre, RS, Brazil e-mail: barbara@if.ufrgs.br
² Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, 1180, Wien, Austria
³ South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
⁴ Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany

Received: 17 September 2005
Accepted: 30 December 2005

Abstract

We studied the class of DB white dwarf stars, using re-calibrated UV spectra for thirty four DBs obtained with the IUE satellite. By comparing the observed energy distributions with model atmospheres, we simultaneously determine spectroscopic distances (d), effective temperature (), and surface gravities (). Using parallax measurements and previous determinations of and from optical spectra, we can study whether the atmospheres of eleven DB stars are consistent with pure He or have a small amount of H contamination. We also report on our observations of seventeen stars with close to the DB instability strip through time series photometry and found them to be non variable within our detection limits.