Asteroseismology of ZZ Ceti stars with full evolutionary white dwarf models

DE GERÓNIMO, F. C.; ALTHAUS, L. G.; CÓRSICO, A. H.; ROMERO, A. D.; KEPLER, S. O.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2018 vol. 613

0004-6361

Context. The thermally pulsing phase on the asymptotic giant branch(TP-AGB) is the last nuclear burning phase experienced by most low- andintermediate-mass stars. During this phase, the outer chemicalstratification above the C/O core of the emerging white dwarf (WD) isbuilt up. The chemical structure resulting from progenitor evolutionstrongly impacts the whole pulsation spectrum exhibited by ZZ Cetistars, which are pulsating C/O core white dwarfs located on a narrowinstability strip at Teff 12 000 K. Several physicalprocesses occurring during progenitor evolution strongly affect thechemical structure of these stars; those found during the TP-AGB phaseare the most relevant for the pulsational properties of ZZ Ceti stars. Aims: We present a study of the impact of the chemical structurebuilt up during the TP-AGB evolution on the stellar parameters inferredfrom asteroseismological fits of ZZ Ceti stars. Methods: Ouranalysis is based on a set of carbon-oxygen core white dwarf models withmasses from 0.534 to 0.6463 M⊙ derived from fullevolutionary computations from the ZAMS to the ZZ Ceti domain. Wecomputed evolutionary sequences that experience different number ofthermal pulses (TP). Results: We find that the occurrence or notof thermal pulses during AGB evolution implies an average deviation inthe asteroseimological effective temperature of ZZ Ceti stars of at most8% and on the order of ≲5% in the stellar mass. For the mass of thehydrogen envelope, however, we find deviations up to 2 orders ofmagnitude in the case of cool ZZ Ceti stars. Hot and intermediatetemperature ZZ Ceti stars show no differences in the hydrogen envelopemass in most cases. Conclusions: Our results show that, ingeneral, the impact of the occurrence or not of thermal pulses in theprogenitor stars is not negligible and must be taken into account inasteroseismological studies of ZZ Ceti stars.