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A Spectroscopic Survey in the EUV of the “Coolest” Hot DA Stars

Published online by Cambridge University Press:  12 April 2016

Jean Dupuis  and
Stéphane Vennes
Jean Dupuis
Affiliation:
Center for EUV Astrophysics, University of California, 2150 Kittredge Street, Berkeley, CA 94720-5030, USA
Stéphane Vennes
Affiliation:
Center for EUV Astrophysics, University of California, 2150 Kittredge Street, Berkeley, CA 94720-5030, USA

Abstract

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We present an analysis of the extreme ultraviolet (EUV) spectroscopy of a sample of 10 DA white dwarfs observed by the Extreme Ultraviolet Explorer (EUVE). We have selected white dwarfs cooler than about 50,000 K and with presumably low heavy element abundances. The goal of this study is to determine the fundamental atmospheric parameters, namely the effective temperature and chemical composition, of these stars by fitting their continua with synthetic spectra computed from pure hydrogen LTE/line-blanketed model atmospheres. The question of the presence (or absence) of trace elements is explored by comparing EUV-determined effective temperatures to the one obtained from a fit of hydrogen balmer lines. It is found that the majority of the DA in the sample are consistent with having a pure hydrogen atmosphere. One of the star, MCT0027-634, is another possible example of a HZ 43-type white dwarf, having an effective temperature above 50000 K and a low heavy element abundance, i.e., much lower than predicted by diffusion theory.

Type
IV. White Dwarf Structure/Evolution
Information
International Astronomical Union Colloquium , Volume 152: Astrophysics in the Extreme Ultraviolet , 1996 , pp. 217 - 222
Copyright
Copyright © Kluwer 1996

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