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Diffusion and Metal Abundances in Hot White Dwarfs Gerard Vauclair

Published online by Cambridge University Press:  12 April 2016

Gérard Vauclair
Gérard Vauclair*
Affiliation:
Observatoire Midi-Pyrénées 14 av. E. Belin, 31400 TOULOUSE, France

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While the efficiency of gravitational settling to produce chemically pure atmospheres in white dwarf stars was outlined for the first time 30 years ago (Schatzman 1958), the competing role of the radiation flux in the hot white dwarfs was considered only 10 years ago (Fontaine and Michaud 1979; Vauclair, Vauclair and Greenstein 1979). At that time, there was more motivation to understand how metals could reappear in the long lived cool non DA white dwarfs, where diffusion time scales are shorter by orders of magnitude than evolutionary time scales. Various processes were invoked to help restore some metal content in the white dwarf atmospheres: convection mixing and dredge up, accretion of interstellar matter. In cool white dwarfs, the radiative acceleration is negligeable in the diffusion process; this is not the case at the hot end of the sequence where radiation may balance gravity. The short lived hot white dwarfs just started to become exciting with the contemporary discoveries that i) some show metallic lines in their spectra, both hydrogen rich and hydrogen poor; ii) some of these are pulsating. In the following years, the number of hot white dwarfs revealing trace abundance of metals has increased, mainly owing to IUE observations.

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 114: White Dwarfs , 1989 , pp. 176 - 187
Copyright
Copyright © Springer-Verlag 1989

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