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Title:
The Effect of Crystallization on the Pulsations of White Dwarf Stars
Authors:
Montgomery, M. H.; Winget, D. E.
Affiliation:
AA(McDonald Observatory and Department of Astronomy, The University of Texas at Austin, Austin, TX 78712.; Institut für Astronomie, Universität Wien, Türkenschanzstraße 17, A-1180 Wien, Austria.), AB(McDonald Observatory and Department of Astronomy, The University of Texas at Austin, Austin, TX 78712.)
Publication:
The Astrophysical Journal, Volume 526, Issue 2, pp. 976-990. (ApJ Homepage)
Publication Date:
12/1999
Origin:
UCP
Astronomy Keywords:
DENSE MATTER, STARS: EVOLUTION, STARS: OSCILLATIONS, STARS: WHITE DWARFS, Dense Matter, Stars: Evolution, Stars: Oscillations, Stars: White Dwarfs
Abstract Copyright:
(c) 1999: The American Astronomical Society
DOI:
10.1086/308044
Bibliographic Code:
1999ApJ...526..976M

Abstract

We consider the pulsational properties of white dwarf star models with temperatures appropriate for the ZZ Ceti instability strip and with masses large enough that they should be substantially crystallized. Our work is motivated by the existence of a potentially crystallized DA variable (DAV), BPM 37093, and the expectation that digital surveys in progress will yield many more such massive pulsators. A crystallized core makes possible a new class of oscillations, the torsional modes, although we expect these modes to couple at most weakly to any motions in the fluid and therefore to remain unobservable. The p-modes should be affected at the level of a few percent in period, but are unlikely to be present with observable amplitudes in crystallizing white dwarfs any more than they are in the other ZZ Ceti's. Most relevant to the observed light variations in white dwarfs are the g-modes. We find that the kinetic energy of these modes is effectively excluded from the crystallized cores of our models. As increasing crystallization pushes these modes farther out from the center, the mean period spacing <ΔP> between radial overtones increases substantially with the crystallized mass fraction, Mcr/M*. In addition, the degree and structure of mode trapping is affected. The fact that some periods are strongly affected by changes in the crystallized mass fraction while others are not suggests that we may be able to disentangle the effects of crystallization from those due to different surface layer masses.
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