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Chemical stratification in white dwarf atmospheres and envelopesTheoretical arguments supporting a new mechanism maintaining a homogeneously mixed composition in white dwarf atmospheres with traces of helium are presented. Diffusion time scales, meridional circulation, mass loss, accretion of interstellar matter, convection, and radiative levitation are discussed. Theoretically, layered envelopes, with hydrogen on top of helium and an abundance profile in the transition layer determined by diffusion equilibrium, are expected. In cases with observed helium and hydrogen in the atmosphere this means that the total hydrogen mass must be very small. The empirical evidence for such atmospheres are assessed, using a new grid of model atmospheres with stratified element abundances and applying it to typical mixed abundance cases at the hot end of the white dwarf temperature sequence.
Document ID
19900045697
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Koester, D.
(Louisiana State University Baton Rouge, United States)
Date Acquired
August 14, 2013
Publication Date
January 1, 1989
Subject Category
Astrophysics
Meeting Information
Meeting: IAU Colloquium
Location: Hanover, NH
Country: United States
Start Date: August 15, 1988
End Date: August 19, 1988
Accession Number
90A32752
Funding Number(s)
CONTRACT_GRANT: NAG5-990
Distribution Limits
Public
Copyright
Other

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