Stars Group : Stellar Pulsation
Thomas G Barnes III
Superintendent McDonald Observatory
Observational aspects of variable stars, particularly distance scale issues for Cepheid and RR Lyrae variables.
Pulsation and seismology of white dwarf stars, nonlinear light curve modeling,
numerical and theoretical studies of convection, evolution of white dwarf stars,
constitutive physics of white dwarfs (crystallization, diffusion), Science Director
of Whole Earth Telescope.
White Dwarfs, Whole Earth Telescope, Asteroseismology
Theory and observation: cosmochronology; evolution of the Milky Way; late stages of stellar evolution; stellar pulsations; white dwarf stars as dark matter detectors; the Whole Earth Telescope.
White Dwarfs, Asteroseismology, Whole Earth Telescope
Thomas G Barnes III, Mike Montgomery, Don Winget
Evidence for Temperature Change and Oblique Pulsation from
Light Curve Fits of the Pulsating White Dwarf GD 358
Convective driving, the mechanism originally proposed by
Brickhill (1991, 1983) for pulsating white dwarf stars, has gained general acceptance as the generic linear instability mechanism in
DAV and DBV white dwarfs. This physical mechanism naturally leads to a nonlinear formulation, reproducing the observed light
curves of many pulsating white dwarfs. This numerical model can also provide information on the average depth of a star's
convection zone and the inclination angle of its pulsation axis. In this paper, we give two sets of results of nonlinear light curve
fits to data on the DBV GD 358. Our first fit is based on data gathered in 2006 by the Whole Earth Telescope (WET); this data set
was multiperiodic, containing at least 12 individual modes. Our second fit utilizes data obtained in 1996, when GD 358 underwent a
dramatic change in excited frequencies accompanied by a rapid increase in fractional amplitude; during this event it was essentially
monoperiodic. We argue that GD 358's convection zone was much thinner in 1996 than in 2006, and we interpret this as a result
of a short-lived increase in its surface temperature. In addition, we find strong evidence of oblique pulsation using two sets of
evenly split triplets in the 2006 data. This marks the first time that oblique pulsation has been identified in a variable white dwarf star.