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T. S. Metcalfe (Harvard-Smithsonian CfA), M. H. Montgomery (U. Cambridge, UK), A. Kanaan (UFSC, Brazil)
More than four decades have passed since it was predicted that the cores of the coolest white dwarf stars should theoretically crystallize. This effect is one of the largest sources of uncertainty in white dwarf cooling models, which are now routinely used to estimate the ages of stellar populations in both the galactic disk and the halo. We are attempting to minimize this source of uncertainty by calibrating the models, using observations of pulsating white dwarfs.
In a typical mass white dwarf model, crystallization does not begin until the surface temperature reaches 6000-8000 K. In more massive white dwarf models the effect begins at higher surface temperatures, where pulsations are observed in the ZZ Ceti (DAV) stars. The most massive DAV white dwarf presently known is BPM 37093. We are using the observed pulsation periods of this star to probe the interior and determine the size of the crystallized core empirically. We will present preliminary results from our application of a genetic-algorithm-based fitting method to address this enormous computational problem.
This research was partially supported by a grant from NASA administered by the American Astronomical Society.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.