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The composition and structure of white dwarf atmospheres revealed by extreme ultraviolet spectroscopyThe ROentgen SATellite (ROSAT) and Extreme UltraViolet Explorer (EUVE) all-sky surveys have resulted in an important change in our understanding of the general composition of hydrogen-rich DA white dwarf atmospheres, with the photospheric opacity dominated by heavy elements rather than helium in the hottest stars (T > 40, 000 K). Most stars cooler than 40,000 K have more or less pure H atmospheres. However, one question, which has not been resolved, concerned the specific nature of the heavy elements and the role of helium in the hottest white dwarfs. One view of white dwarf evolution requires that H-rich DA stars form by gravitational settling of He from either DAO or He-rich central stars of planetary nebulae. In this case, the youngest (hottest) DA white dwarfs may still contain visible traces of He. Spectroscopic observations now available with EUVE provide a crucial test of these ideas. Analysis of data from the EUVE Guest Observer programme and EUVE public archive allows quantitative consideration of the sources of EUV opacity and places limits on the abundance of He which may be present.
Document ID
19990116567
Acquisition Source
Headquarters
Document Type
Conference Paper
Authors
Barstow, Martin A.
(Leicester Univ. United Kingdom)
Hubeny, Ivan
(Universities Space Research Association Greenbelt, MD United States)
Lanz, Thierry
(Universities Space Research Association Greenbelt, MD United States)
Holberg, Jay B.
(Arizona Univ. Tucson, AZ United States)
Sion, Edward M.
(Villanova Univ. PA United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 1995
Publication Information
Publication: Papers presented at IAU colloquium No. 152: Astrophysics in the Extreme Ultaviolet
Subject Category
Astronomy
Funding Number(s)
CONTRACT_GRANT: NAGw-5716
CONTRACT_GRANT: NAGw-3834
Distribution Limits
Public
Copyright
Other
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