Evolution and chemical yields of AGB stars: effects of low-temperature opacities

TL;DR

This paper investigates how using updated low-temperature opacities, which account for surface chemical changes, affects the evolution and chemical yields of AGB stars, highlighting the importance of accurate opacity modeling.

Contribution

It introduces new molecular opacities computed with AESOPUS into stellar models to assess their impact on AGB star evolution and yields, emphasizing the need for revised models.

Findings

Models with updated opacities show significant differences in chemical yields.

Many existing models require revision due to inadequate opacity assumptions.

The interplay of convection, hot-bottom burning, and opacities critically affects predictions.

Abstract

The studies focused on the Thermally-Pulsing Asymptotic Giant Branch phase experienced by low- and intermediate-mass stars are extremely important in many astrophysical contexts. In particular, a detailed computation of their chemical yields is essential for several issues, ranging from the chemical evolution of galaxies, to the mechanisms behind the formation of globular clusters. Among all the uncertainties affecting the theoretical modelling of this phase, and described in the literature, it remains to be fully clarified which results are severely affected by the use of inadequate low-temperature opacities, that are in most cases calculated on the basis of the original chemical composition of the stars, and do not consider the changes in the surface chemistry due to the occurrence of the third dredge-up and hot-bottom burning. Our investigation is aimed at investigating this point. By means of full evolutionary models including new set of molecular opacities computed specifically with the AESOPUS tool, we highlight which stellar models, among those present in the literature, need a substantial revision, mainly in relation to the predicted chemical yields. The interplay among convection, hot bottom burning and the low-temperature opacity treatment is also discussed