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

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

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2017 vol. 607

0004-6361

Context. Many pulsating low-mass white dwarf stars have been detected inthe past years in the field of our Galaxy. Some of them exhibitmultiperiodic brightness variation, therefore it is possible to probetheir interiors through asteroseismology. Aims: We present adetailed asteroseismological study of all the known low-mass variablewhite dwarf stars based on a complete set of fully evolutionary modelsthat are representative of low-mass He-core white dwarf stars. Methods: We employed adiabatic radial and nonradial pulsation periodsfor low-mass white dwarf models with stellar masses ranging from 0.1554to 0.4352 M⊙ that were derived by simulating thenonconservative evolution of a binary system consisting of an initially1 M⊙ zero-age main-sequence (ZAMS) star and a 1.4M⊙ neutron star companion. We estimated the mean periodspacing for the stars under study (where this was possible), and then weconstrained the stellar mass by comparing the observed period spacingwith the average 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 representativeseismological model. Results: We found that even though the starsunder analysis exhibit few periods and the period fits show multiplicityof solutions, it is possible to find seismological models whose mass andeffective temperature are in agreement with the values given byspectroscopy for most of the cases. Unfortunately, we were not able toconstrain the stellar masses by employing the observed period spacingbecause, in general, only few periods are exhibited by these stars. Inthe two cases where we were able to extract the period spacing from theset of observed periods, this method led to stellar mass values thatwere substantially higher than expected for this type of stars. Conclusions: The results presented in this work show the need forfurther photometric searches, on the one hand, and that someimprovements of the theoretical models are required on the other hand inorder to place the asteroseismological results on a firmer ground.