On the evolution of ultra-massive white dwarfs

M.E. CAMISASSA; L.G. ALTHAUS; A.H. CÓRSICO ; F.C. DE GERÓNIMO; M. M. MILLER BERTOLAMI ; M.L. NOVARINO; R.D. ROHRMANN; F.C. WACHLIN; E. GARCÍA BERRO

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2018

0004-6361

Context: White dwarfs are nowadays routinely used as reliable cosmochronometers, allowing to date several stellar populations. Inparticular, ultra-massive white dwarfs are involved in other various applications which include physical processes in the AsymptoticGiant Branch (AGB), the theory of crystallization and type Ia supernova explosions.Aims: Despite the interest in these white dwarfs, there are few evolutionary studies in the literature devoted to them. Here, we presentnew ultra-massive white dwarf evolutionary sequences that constitute an improvement over previous ones.Methods: In these new sequences, we take into account for the first time the process of phase separation expected during the crys-tallization stage of these white dwarfs, by relying on the most up-to-date phase diagram of dense oxygen/neon mixtures. Realisticchemical profiles resulting from the full computation of progenitor evolution during the semidegenerate carbon burning along thesuper-AGB phase are also considered in our sequences. Outer boundary conditions for our evolving models are provided by detailednon-gray white dwarf model atmospheres for hydrogen and helium composition.Results: We assessed the impact of all these improvements on the evolutionary properties of ultra-massive white dwarfs, providingup-dated evolutionary sequences for these stars.Conclusions. These white dwarf sequences provide a new theoretical frame to perform asteroseismological studies on the recentlydetected ultra-massive pulsating white dwarfs.