Pulsating low-mass white dwarfs in the frame of new evolutionary sequences. V. Asteroseismology of ELMV white dwarf stars

CALCAFERRO, L. M.; CÓRSICO, A. H.; ALTHAUS, L. G.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: París; Año: 2017 vol. 607

0004-6361

Context. Many pulsating low-mass white dwarf stars have been detected in the past years in the field of our Galaxy. Some of themexhibit multiperiodic brightness variation, therefore it is possible to probe their interiors through asteroseismology.Aims. We present a detailed asteroseismological study of all the known low-mass variable white dwarf stars based on a complete setof fully evolutionary models that are representative of low-mass He-core white dwarf stars.Methods. We employed adiabatic radial and nonradial pulsation periods for low-mass white dwarf models with stellar masses rangingfrom 0.1554 to 0.4352 M that were derived by simulating the nonconservative evolution of a binary system consisting of an initially1 M zero-age main-sequence (ZAMS) star and a 1.4 M neutron star companion. We estimated the mean period spacing for the starsunder study (where this was possible), and then we constrained the stellar mass by comparing the observed period spacing with theaverage of the computed period spacings for our grid of models. We also employed the individual observed periods of every knownpulsating low-mass white dwarf star to search for a representative seismological model.Results. We found that even though the stars under analysis exhibit few periods and the period fits show multiplicity of solutions, it ispossible to find seismological models whose mass and effective temperature are in agreement with the values given by spectroscopyfor most of the cases. Unfortunately, we were not able to constrain the stellar masses by employing the observed period spacingbecause, in general, only few periods are exhibited by these stars. In the two cases where we were able to extract the period spacingfrom the set of observed periods, this method led to stellar mass values that were substantially higher than expected for this type ofstars.Conclusions. The results presented in this work show the need for further photometric searches, on the one hand, and that someimprovements of the theoretical models are required on the other hand in order to place the asteroseismological results on a firmerground.