Updated Low-temperature Gas Opacities with ÆSOPUS 2.0

Abstract

Abstract This work introduces new low-temperature gas opacities in the range 3.2 ≲ log ( T / K ) ≲ 4.5 computed with the ÆSOPUS code under the assumption of thermodynamic equilibrium. In comparison to the previous version, ÆSOPUS 1.0, we updated and expanded molecular absorption to include 80 species, mostly using the recommended line lists currently available from the ExoMol and HITRAN databases. Furthermore, in light of a recent study, we revised the H− photodetachment cross section, added the free–free absorption of other negative ions of atoms and molecules, and updated the collision-induced absorption due to H2/H2, H2/H, H2/He, and H/He pairs. Using the new input physics, we computed tables of Rosseland mean opacities for several scaled-solar chemical compositions, including Magg et al.'s most recent one, as well as α-enhanced mixtures. The differences in opacity between the new ÆSOPUS 2.0 and the original ÆSOPUS 1.0 versions, as well as other sets of calculations, are discussed. The new opacities are released to the community via a dedicated webpage that includes both precomputed tables for widely used chemical compositions and a web interface for calculating opacities on the fly for any abundance distribution.