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Atsuko Nitta, D. E. Winget (U. Texas at Austin), S.O. Kepler (UFRGS, Brazil)
The cool white dwarf stars are among the oldest population of stars in our galaxy. White dwarf evolution is dominated by cooling; there is a simple relation between effective temperature and age. With an accurate understanding of the physics that takes place inside the cool white dwarfs, we can estimate the age of the galactic disk. Here, we present our work in two different areas regarding the cool white dwarfs: first using a pulsating massive white dwarf (BPM37093) to test the theory of internal crystallization via asteroseismology, and second by searching for a new class of cool white dwarf pulsators.
A major mystery surrounding white dwarfs is what decides their surface chemical composition. Two major spectroscopic types of white dwarfs are the hydrogen rich DAs to which 75% of the white dwarfs belong to, and the helium rich atmosphere (DBs.) The origin of this bifurcation is still not known. The pulsating white dwarfs are otherwise normal white dwarfs. Hence whatever we learn from the pulsators are applicable to the non-pulsating white dwarfs as well. We have studied four (GD358, PG1351, PG1551, EC20058) out of eight DB pulsators known using the Whole Earth Telescope data in hopes of understanding the cause of this bifurcation.