New Chemical Profiles for the Asteroseismology of ZZ Ceti Stars

ALTHAUS, L. G.; CÓRSICO, A. H.; BISCHOFF-KIM, A.; ROMERO, A. D.; RENEDO, I.; GARCÍA-BERRO, E.; MILLER BERTOLAMI, M. M.

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Bristol; Año: 2010 vol. 717 p. 897 - 907

0004-637X

We compute new chemical profiles for the core and envelope of white dwarfs appropriate for pulsational studiesof ZZ Ceti stars. These profiles are extracted from the complete evolution of progenitor stars, evolved throughthe main sequence and the thermally pulsing asymptotic giant branch (AGB) stages, and from time-dependentelement diffusion during white dwarf evolution. We discuss the importance of the initial–final mass relationshipfor the white dwarf carbon–oxygen composition. In particular, we find that the central oxygen abundance maybe underestimated by about 15% if the white dwarf mass is assumed to be the hydrogen-free core mass beforethe first thermal pulse. We also discuss the importance for the chemical profiles expected in the outermost layersof ZZ Ceti stars of the computation of the thermally pulsing AGB phase and of the phase in which elementdiffusion is relevant. We find a strong dependence of the outer layer chemical stratification on the stellar mass.In particular, in the less massive models, the double-layered structure in the helium layer built up during thethermally pulsing AGB phase is not removed by diffusion by the time the ZZ Ceti stage is reached. Finally,we perform adiabatic pulsation calculations and discuss the implications of our new chemical profiles for thepulsational properties of ZZ Ceti stars. We find that the whole g-mode period spectrum and the mode-trappingproperties of these pulsating white dwarfs as derived from our new chemical profiles are substantially differentfrom those based on chemical profiles widely used in existing asteroseismological studies. Thus, we expect theasteroseismological models derived from our chemical profiles to be significantly different from those found thus far.