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EDP Sciences, Astronomy & Astrophysics, 1(432), p. 219-224, 2005

DOI: 10.1051/0004-6361:20041125

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Whole Earth Telescope observations of BPM 37093: a seismological test of crystallization theory in white dwarfs

Journal article published in 2005 by R. �stensen, A. Kanaan, Atsuko Nitta, Donald Earl Winget, Souza Oliveira Kepler, J. E. S. Costa, Michael Houston Montgomery, Travis S. Metcalfe, H. Oliveira, Luciano Fraga, A. F. M. da Costa, Alex Fabiano Murillo da Costa, Bárbara Garcia Castanheira, Jose Eduardo da Silveira Costa, Odilon Giovannini and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

BPM 37093 is the only hydrogen-atmosphere white dwarf currently known which has sufficient mass (~1.1 MO) to theoretically crystallize while still inside the ZZ Ceti instability strip (Teff ~ 12 000 K). As a consequence, this star represents our first opportunity to test crystallization theory directly. If the core is substantially crystallized, then the inner boundary for each pulsation mode will be located at the top of the solid core rather than at the center of the star, affecting mainly the average period spacing. This is distinct from the “mode trapping” caused by the stratified surface layers, which modifies the pulsation periods more selectively. In this paper we report on Whole Earth Telescope observations of BPM 37093 obtained in 1998 and 1999. Based on a simple analysis of the average period spacing we conclude that a large fraction of the total stellar mass is likely to be crystallized. ; The definitive version of this paper is available from www.aanda.org