Evolutionary and pulsational properties of ultra-massive white dwarfs with Oxygen-Neon cores: The role of crystallization

ALTHAUS, L. G.; DE GERÓNIMO, F. C.; WACHLIN, F. C.; CAMISASSA, M. E.; CAMISASSA, MARÍA E.

Austin, Texas

Workshop; 21st European White Dwarf Workshop; 2018

Ultra-massive hydrogen-rich white dwarfs stars are expected to harbour oxygen/neon cores resulting from semidegenerate carbon burning when the progenitor star  evolves through the super asymptotic giant branch (S-AGB) 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 white dwarfs, which impacts markedly the pulsational properties, thus offering a unique opportunity to infer and test   the process of crystallization and phase separation in white dwarf stars.