A New Generation of Cool White Dwarf Atmosphere Models Using Ab Initio Calculations

TL;DR

This paper develops advanced atmosphere models for cool helium-rich white dwarfs using ab initio calculations, revealing significant effects of high density on metal ionization and collision-induced absorption spectra.

Contribution

It introduces a new generation of atmosphere models incorporating ab initio calculations to account for high-density effects in cool white dwarf atmospheres.

Findings

Ionization of metals is inhibited at high densities.

H$_2$-He CIA spectrum is significantly distorted at densities above 0.1 g/cm$^3$.

Models improve understanding of dense white dwarf atmospheres.

Abstract

Due to their high photospheric density, cool helium-rich white dwarfs (particularly DZ, DQpec and ultracool) are often poorly described by current atmosphere models. As part of our ongoing efforts to design atmosphere models suitable for all cool white dwarfs, we investigate how the ionization ratio of heavy elements and the H$_2$-He collision-induced absorption (CIA) spectrum are altered under fluid-like densities. For the conditions encountered at the photosphere of cool helium-rich white dwarfs, our ab initio calculations show that the ionization of most metals is inhibited and that the H$_2$-He CIA spectrum is significantly distorted for densities higher than 0.1 g/cm$^3$.