Low temperature mean opacities for the carbon-rich regime

TL;DR

This paper provides new low-temperature mean opacity tables for carbon-rich and oxygen-rich AGB star envelopes, enabling more accurate stellar evolution modeling of chemical composition changes.

Contribution

It introduces a comprehensive set of opacity tables covering both C/O regimes, improving upon previous data limited to scaled solar compositions.

Findings

New opacity tables for C/O < 1 and C/O > 1 regimes

Comparison shows differences with existing data

Analysis of molecular contributors to opacity

Abstract

Asymptotic Giant Branch (AGB) stars undergo a change in their chemical composition during their evolution. This in turn leads to an alteration of the radiative opacities, especially in the cool layers of the envelope and the atmosphere, where molecules are the dominant opacity sources. A key parameter in this respect is the number ratio of carbon to oxygen atoms (C/O). In terms of low temperature mean opacities, a variation of this parameter usually cannot be followed in stellar evolution models, because up to now tabulated values were only available for scaled solar metal mixtures (with C/O ~ 0.5). We thus present a set of newly generated tables containing Rosseland mean opacity coefficients covering both the oxygen-rich (C/O < 1) and the carbon-rich (C/O > 1) regime. We compare our values to existing tabular data and investigate the relevant molecular opacity contributors.