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New model atmospheres for very cool white dwarfs with mixed H/He and pure He compositionsNew model atmosphere calculations for very cool white dwarfs with mixed H/He and pure He compositions are presented. The hydrogen-rich models incorporate improved cross section calculations of the collision-induced absorption by molecular hydrogen due to collisions with H2, H, and He. The effects associated with variations in the effective temperature (T(sub eff) greater than or equal to 4000 and less than or equal to 10,000 K), the surface gravity (log g greater than or equal to 7.5 and less than or equal to 9.5), and the chemical composition (N(He)/N(H) greater than or equal to O and less than or equal to 100) are investigated. Results from earlier calculations are confirmed qualitatively, but a more detailed comparison reveals large quantitative deviations. Cool white dwarfs with mixed H/He chemical compositions are shown to be easily recognizable from their predicted strong infrared flux deficiency. Pure helium model calculations are described as well. These include a modified version of the recently developed equation of state of D. Saumon and G. Chabrier. Nonideal effects brought about by various equations of state are explored in detail. For the purpose of this analysis, a model of pressure ionization based on an accurate description of the interactions in a mostly atomic helium fluid is developed. The effects of pressure ionization are shown to be the most important issue in the model calculations. A critical discussion of previous generations of pure helium model calculations is presented. Finally, broadband color indices are provided for the complete model grid.
Document ID
19950054625
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Bergeron, P.
(Universite de Montreal Montreal, Quebec, Canada)
Saumon, D.
(University of Arizona, Tucson, AZ United States)
Wesemael, F.
(Universite de Montreal Montreal, Quebec, Canada)
Date Acquired
August 16, 2013
Publication Date
April 20, 1995
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 443
Issue: 2
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A86224
Funding Number(s)
CONTRACT_GRANT: NAS5-26555
CONTRACT_GRANT: NSF AST-89-10780
Distribution Limits
Public
Copyright
Other

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