Time dependent diffusion in pulsating white dwarf stars: Asteroseismology of G117-B15A

Abstract

We study the structural characteristic of the variable DA white dwarf G117B-15A by applying the methods of asteroseismology. For such a purpose, we construct white dwarf evolutionary models considering a detailed and up-to-date physical description as well as several processes responsible for the occurrence of element diffusion. We have considered several thickness for the outermost hydrogen layer, whereas for the inner helium-, carbon- and oxygen-rich layers we considered realistic profiles predicted by calculations of the white dwarf progenitor evolution. The evolution of each of the considered model sequences were followed down to very low effective temperature; in particular, from 12500K on we computed the dipolar, linear, adiabatic oscillations with low radial order. We find that asteroseismological results are not univocal regarding mode identification for the case of G117B-15A. However, our asteroseismological results are compatible with spectroscopical data only if the observed periods of 215.2, 271.0 and 304.4 s are due to dipolar modes with $k=2,3,4$ respectively. Our calculations indicate that the best fit to the observed period pattern of G117B-15A corresponds to a DA white dwarf structure with a stellar mass of 0.525 \msun, with a hydrogen mass fraction \lmh$\gtrsim$-3.83 at an effective temperature \teff$\approx$11800K.

8 pages, 8 figures, to be published in MNRAS

References in corpus (4)

• Diffusion and the occurrence of hydrogen shell flashes in helium white dwarf stars
• The potential of the variable DA white dwarf G117-B15A as a tool for Fundamental Physics
• Preliminary Constraints on 12C(alpha,gamma)16O from White Dwarf Seismology
• The Effects of Element Diffusion on the Pulsational Properties of Variable DA White Dwarf Stars

Cited by in corpus (11)

• Evolutionary and pulsational properties of white dwarf stars
• Pulsating White Dwarf Stars and Precision Asteroseismology
• Toward ensemble asteroseismology of ZZ Ceti stars with fully evolutionary models
• Measuring the evolution of the most stable optical clock G 117-B15A
• New chemical profiles for the asteroseismology of ZZ Ceti stars
• Seismological studies of ZZ Ceti stars. I. The model grid and the application to individual stars
• Observational Constraints on the Degenerate Mass-Radius Relation
• Fine Grid Asteroseismology of R548 and G117-B15A
• The pulsating white dwarf G117-B15A: still the most stable optical clock known
• On mode trapping in pulsating DA white dwarf stars
• The rate of period change in DAV stars