The updated BaSTI stellar evolution models and isochrones. III. White Dwarfs

TL;DR

This paper introduces updated white dwarf cooling models within the BaSTI stellar evolution archive, incorporating new physics, chemical stratifications, and opacity choices, to improve understanding of white dwarf evolution across different populations.

Contribution

It provides new, comprehensive white dwarf models with updated physics and multiple opacity options, extending the BaSTI archive for diverse stellar populations.

Findings

Inclusion of ^{22}Ne diffusion and updated phase diagrams improves model accuracy.

Models cover a wide range of neon abundances for different metallicities.

Preliminary assessment shows Fe sedimentation has a small effect on cooling times.

Abstract

We present new cooling models for carbon-oxygen white dwarfs with both H- and He-atmospheres, covering the whole relevant mass range, to extend our updated BaSTI (a Bag of Stellar Tracks and Isochrones) stellar evolution archive. They have been computed using core chemical stratifications obtained from new progenitor calculations, adopting a semiempirical initial-final mass relation. The physics inputs have been updated compared to our previous BaSTI calculations: ^{22}Ne diffusion in the core is now included, together with an updated CO phase diagram, and updated electron conduction opacities. We have calculated models with various different neon abundances in the core, suitable to study white dwarfs in populations with metallicities ranging from super-solar to metal poor, and have performed various tests/comparisons of the chemical stratification and cooling times of our models. Two complete sets of calculations are provided, for two different choices of the electron conduction opacities, to reflect the current uncertainty in the evaluation of the electron thermal conductivity in the transition regime between moderate and strong degeneracy, crucial for the H and He envelopes. We have also made a first, preliminary estimate of the effect -- that turns out to be generally small -- of Fe sedimentation on the cooling times of white dwarf models, following recent calculations of the phase diagrams of carbon-oxygen-iron mixtures. We make publicly available the evolutionary tracks from both sets of calculations, including cooling times and magnitudes in the Johnson-Cousins, Sloan, Pan-STARSS, Galex, Gaia-DR2, Gaia-eDR3, HST-ACS, HST-WFC3, and JWST photometric systems.