New Conductive Opacities for White Dwarf Envelopes

TL;DR

This paper introduces improved conductive opacities for white dwarf envelopes, significantly affecting cooling models and age estimates, with differences up to a factor of 3 from previous models, thereby refining white dwarf cosmochronology.

Contribution

The authors present new conductive opacity calculations for white dwarf envelopes, incorporating better electron-electron scattering treatment, and provide analytical fits for easier implementation in models.

Findings

Up to a factor of 3 difference from previous opacities.

White dwarf age estimates can decrease by up to 2 Gyr with new opacities.

Analytical fits provided for model integration.

Abstract

Thanks to their continuous cooling and relative simplicity, white dwarf stars are routinely used to measure the ages of stellar populations. The usefulness of white dwarfs as cosmochronometers depends on the availability of accurate cooling models. A key ingredient of those models are the conductive opacities, which largely govern the cooling rate. In this work, we present improved conductive opacities for the regime of moderate coupling and moderate degeneracy that characterizes an important portion of the envelopes of DA and DB white dwarfs. We find differences of up to a factor 3 between our calculations and the commonly used opacities of Cassisi et al. (2007), which we attribute to an improved account of electron-electron scattering. The cooling models are strongly affected by those changes in the conductive opacities: the age of a 4000 K white dwarf can be reduced by as much as 2 Gyr. We provide analytical fits to our new opacities to facilitate the implementation of this important effect in white dwarf evolution codes.