Evolutionary and pulsational properties of ultra-massive white dwarfs. The role of oxygen-neon phase separation

TL;DR

This paper investigates how oxygen-neon phase separation during crystallization affects the pulsational properties of ultra-massive white dwarfs, providing insights into their core composition and crystallization processes.

Contribution

It introduces the impact of oxygen-neon phase separation on pulsations in ultra-massive white dwarfs, linking core chemistry with observable properties.

Findings

Crystallization causes oxygen-neon phase separation in ultra-massive WDs.

Phase separation significantly alters pulsational characteristics.

Results enable probing of WD core composition through pulsation analysis.

Abstract

Ultra-massive hydrogen-rich white dwarfs (WDs) stars are expected to harbor oxygen/neon cores resulting from semi-degenerate carbon burning when the progenitor star evolves through the super asymptotic giant branch (SAGB) phase. These stars are expected to be crystallized by the time they reach the ZZ Ceti domain. We show that crystallization leads to a phase separation of oxygen and neon in the core of ultra-massive WDs, which impacts markedly the pulsational properties, thus offering a unique opportunity to study the processes of crystallization and to infer the core chemical composition in WD stars.