Evolution and Asteroseismology of Pulsating Low-Mass White Dwarfs

TL;DR

This study uses detailed asteroseismological models to analyze low-mass white dwarfs, revealing that some have thick hydrogen envelopes while others have thin ones, challenging previous assumptions.

Contribution

It introduces a comprehensive set of evolutionary models with varied hydrogen envelope thicknesses to better interpret pulsating low-mass white dwarfs.

Findings

Some stars have thick hydrogen envelopes.

Others are better modeled with thin hydrogen envelopes.

Expands the parameter space for white dwarf asteroseismology.

Abstract

Many low-mass white dwarfs are being discovered in the field of our galaxy and some of them exhibit $g$-mode pulsations, comprising the extremely low-mass variable (ELMV) stars class. Despite it is generally believed that these stars are characterized by thick H envelopes, from stellar evolution considerations, the existence of low-mass WDs with thin H envelopes is also possible. We have performed detailed asteroseismological fits to all the known ELMVs to search for a representative model by employing a set of fully evolutionary models that are representative of low-mass He-core white dwarf stars with a range of stellar masses $[0.1554-0.4352]\ M_{\odot}$, effective temperatures $[6000-10000]\ $K, and also with a range of H envelope thicknesses $-5.8 \lesssim \log(M_{\rm H}/M_{\star}) \lesssim -1.7$, hence expanding the space of parameters. We found that some of the stars under analysis are characterized by thick H envelopes, but others are better represented by models with thin H envelope.