On the possibility of using seismic probes to study the core composition in pulsating white dwarfs

TL;DR

This paper explores how seismic oscillation modes in pulsating white dwarfs can reveal their core chemical composition, potentially enabling seismic probing of their internal structure.

Contribution

It demonstrates that core chemical stratification affects p-mode frequencies in white dwarfs and provides an analytical model for interpreting seismic signals.

Findings

Seismic signals depend on core composition

Analytical model links frequency modulations to chemical stratification

Potential to determine core structure from pulsation data

Abstract

White dwarfs correspond to the final stages of stellar evolution of solar-type stars. In these objects, production of energy by nuclear burning has ended which means that a white dwarf simply cools down over the course of the next billion years. It is now known that white dwarfs spend some of their cooling history in an instability strip. The pulsating white dwarfs with an hydrogen atmosphere (called DAV or ZZ Ceti stars) show non-radial oscillation modes with periods in the range 100 - 1200s. In this work we try to illustrate how the oscillation p-mode frequencies of idealized white dwarf models change as the result of a different chemical composition in the core, with the ultimate goal of determining the chemical stratification from seismic observations. The presence of acoustic glitches in the internal structure results in a periodic signal in the frequencies. We find that this signal depends on the chemical stratification/composition of the core in a form that can be analytically modelled.