New evolutionary models for massive ZZ Ceti stars. II. The effects of crystallization on their pulsational properties

Abstract

We present in this work new pulsational calculations for improved carbon-oxygen DA white dwarf models suitable for the study of massive ZZ Ceti stars. The background models employed in this study, presented in detail in a recent paper by Althaus et al. (2003), are the result of the complete evolution of massive white dwarf progenitors from the zero-age main sequence through the Asymptotic Giant Branch (AGB) and mass loss phases to the white dwarf regime. Abundance changes are accounted for by means of a full coupling between nuclear evolution and time-dependent mixing due to convection, salt fingers, and diffusive overshoot. In addition, time-dependent element diffusion for multicomponent gases has been considered during the white dwarf evolution. Crystallization and chemical rehomogenization due to phase separation upon crystallization in the core of our models have been fully considered. The effects of crystallization on the period spectrum of these massive white dwarf models are assessed by means of a detailed pulsational analysis. We find that the theoretical pulsation spectrum is strongly modified when crystallization is considered, in particular concerning the mode trapping properties of the equilibrium models. We also discuss at some length the implications of our study for BPM 37093, the most massive ZZ Ceti star presently known. We find that if BPM 37093 has a stellar mass of $\approx 1.00$ \msun its observed spectrum could bear the signature of overshoot episodes during the helium core burning.

15 Pages, including 17 Postscript figures. Accepted for publication in Astronomy and Astrophysics

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• Asteroseismic inferences on GW Vir variable stars in the frame of new PG 1159 evolutionary models
• New chemical profiles for the asteroseismology of ZZ Ceti stars
• Asteroseismological study of massive ZZ Ceti stars with fully evolutionary models
• Asteroseismology of ZZ Ceti stars with fully evolutionary white dwarf models: I. The impact of the uncertainties from prior evolution on the period spectrum
• The formation of ultra-massive carbon-oxygen core white dwarfs and their evolutionary and pulsational properties
• Pulsation properties of ultra-massive DA white dwarf stars with ONe cores
• Asteroseismology of hybrid $\delta$ Scuti--$\gamma$ Doradus pulsating stars
• Probing the structure of Kepler ZZ Ceti stars with full evolutionary models-based asteroseismology
• Asteroseismological analysis of the ultra-massive ZZ Ceti stars BPM~37093, GD~518, and SDSS~J0840+5222
• Asteroseismology of ZZ Ceti stars with full evolutionary white dwarf models. II. The impact of AGB thermal pulses on the asteroseismic inferences of ZZ Ceti stars
• WD J004917.14$-$252556.81, the Most Massive Pulsating White Dwarf
• Asteroseismology of Pulsating Stars
• Oscillations and tidal deformations of crystallized white dwarfs
• Astrophysics in 2005
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• The pulsational properties of ultra-massive DB white dwarfs with carbon-oxygen cores coming from single-star evolution
• The gravitational wave radiation of pulsating white dwarfs revisited: the case of BPM 37093 and PG 1159-035
• Seismology and diffusion of ultramassive white dwarf magnetic fields