An asteroseismic test of diffusion theory in white dwarfs

Abstract

The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens as the star cools. In the temperature range of the pulsating DB white dwarfs (T_eff ~ 25,000 K) this transformation is still taking place, allowing asteroseismic tests of the theory. We have obtained dual-site observations of the pulsating DB star CBS114, to complement existing observations of the slightly cooler star GD358. We recover the 7 independent pulsation modes that were previously known, and we discover 4 new ones to provide additional constraints on the models. We perform objective global fitting of our updated double-layered envelope models to both sets of observations, leading to determinations of the envelope masses and pure He surface layers that qualitatively agree with the expectations of diffusion theory. These results provide new asteroseismic evidence supporting one of the central assumptions of spectral evolution theory, linking the DB white dwarfs to PG1159 stars.

7 pages, 3 figures, 3 tables, accepted for publication in A&A

References in corpus (13)

• A Catalog of Spectroscopically Identified White Dwarf Stars in the First Data Release of the Sloan Digital Sky Survey
• Stellar Structure Modeling using a Parallel Genetic Algorithm for Objective Global Optimization
• Combination Frequencies in the Fourier Spectra of White Dwarfs
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• The core/envelope symmetry in pulsating stars
• A CCD Time-Series Photometer
• White Dwarf Asteroseismology and the ^12C(alpha,gamma)^16O Rate
• The Everchanging Pulsating White Dwarf GD358
• Probing the core and envelope structure of DBV white dwarfs
• Nonlinear effects in time-resolved spectra of DAVs
• The double-layered chemical structure in DB white dwarfs
• The asteroseismological potential of the pulsating DB white dwarf stars CBS 114 and PG 1456+103
• A new look at the pulsating DB white dwarf GD 358:Line-of-sight velocity measurements and constraints on model atmospheres

Cited by in corpus (7)

• White Dwarf Mass Distribution in the SDSS
• The Element Abundances in Bare Planetary Nebula Central Stars and the Shell Burning in AGB Stars
• New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey
• A deeper understanding of white dwarf interiors
• Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058-5234
• Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067
• Asteroseismology of the DBV star CBS 114