Infrared Opacities in Dense Atmospheres of Cool White Dwarf Stars

TL;DR

This paper uses computational quantum chemistry to model infrared opacities in dense, helium-rich atmospheres of cool white dwarfs, addressing previous modeling challenges and improving spectral analysis accuracy.

Contribution

It introduces quantum chemistry simulations to accurately model IR opacities in dense white dwarf atmospheres, accounting for multi-atomic interactions.

Findings

Significant IR absorption from He atoms (He-He-He CIA)

Pressure distortion of H₂-He collision-induced absorption

Improved spectral fitting for cool, He-rich white dwarfs

Abstract

Dense, He-rich atmospheres of cool white dwarfs represent a challenge to the modeling. This is because these atmospheres are constituted of a dense fluid in which strong multi-atomic interactions determine their physics and chemistry. Therefore, the ideal-gas-based description of absorption is no longer adequate, which makes the opacities of these atmospheres difficult to model. This is illustrated with severe problems in fitting the spectra of cool, He-rich stars. Good description of the infrared (IR) opacity is essential for proper assignment of the atmospheric parameters of these stars. Using methods of computational quantum chemistry we simulate the IR absorption of dense He/H media. We found a significant IR absorption from He atoms (He-He-He CIA opacity) and a strong pressure distortion of the H$_2$-He collision-induced absorption (CIA). We discuss the implication of these results for interpretation of the spectra of cool stars.