Asteroseismology of the ZZ Ceti star HS 0507+0434B

TL;DR

This study conducts a detailed asteroseismological analysis of the ZZ Ceti star HS 0507+0434B, revealing its internal structure, rotation, and fundamental parameters through extensive multisite photometric observations and Fourier analysis.

Contribution

It provides the first detailed asteroseismological model of HS 0507+0434B, including mode identification, rotation rate, and internal structure constraints, based on extensive observational data.

Findings

39 resolved frequencies including triplets and linear combinations

Identification of $ ext{l}=1$ g-modes and measurement of rotational splitting

Estimated stellar parameters: mass 0.675 M_sun, luminosity 3.5e-3 L_sun, hydrogen mass fraction 10^-8.5

Abstract

The pulsating DA white dwarfs (ZZ Ceti stars) are $g$-mode non-radial pulsators. Asteroseismology provides strong constraints on their global parameters and internal structure. Since all the DA white dwarfs falling in the ZZ Ceti instability strip do pulsate, the internal structure derived from asteroseismology brings knowledge for the DA white dwarfs as a whole group. HS 0507+0434B is one of the ZZ Ceti stars which lies approximately in the middle of the instability strip for which we have undertaken a detailed asteroseismological study. We carried out multisite observation campaigns in 2007 and from December 2009 to January 2010. In total, 206 hours of photometric time-series have been collected. They have been analysed by means of Fourier analysis and simultaneous multi-frequency sine-wave fitting. In total, 39 frequency values are resolved including 6 triplets and a number of linear combinations. We identify the triplets as $\ell$=1 $g$-modes split by rotation. We derived the period spacing, the rotational splitting and the rotation rate. From the comparison of the observed periods with the theoretical periods of a series of models we estimate the fundamental parameters of the star: its total mass M$_{*}$/M$_{\odot}$ = 0.675, its luminosity L/L$_{\odot}$=3.5$\times 10^{-3}$, and its hydrogen mass fraction M$_{H}$/M$_{*}$= 10$^{-8.5}$.