Yields of AGB and SAGB models with chemistry of low- and high-metallicity Globular Clusters

TL;DR

This study provides detailed stellar yields for intermediate-mass stars at different metallicities, highlighting how processes like Third Dredge-Up and Hot Bottom Burning influence chemical enrichment relevant to globular cluster evolution.

Contribution

It offers new stellar yield models across low and high metallicities, incorporating full evolutionary calculations from pre-Main Sequence to AGB phase, emphasizing the impact of metallicity on nucleosynthesis processes.

Findings

Hot Bottom Burning depends strongly on metallicity.

Stars with M<3Mo mainly eject carbon and nitrogen.

Mass loss and convection are key uncertainties in models.

Abstract

We present yields from stars of mass in the range Mo<M<8Mo of metallicities Z=0.0003 and Z=0.008, thus encompassing the chemistry of low- and high-Z Globular Clusters. The yields are based on full evolutionary computations, following the evolution of the stars from the pre-Main Sequence through the Asymptotic Giant Branch phase, until the external envelope is lost. Independently of metallicity, stars with M<3Mo are dominated by Third Dredge-Up, thus ejecting into their surroundings gas enriched in carbon and nitrogen. Conversely, Hot Bottom Burning is the main responsible for the modification of the surface chemistry of more massive stars, whose mass exceeds 3Mo: their gas shows traces of proton-capture nucleosynthesis. The extent of Hot Bottom Burning turns out to be strongly dependent on metallicity. In this paper we analyze the consequences of this fact. These results can be used to understand the role played by intermediate mass stars in the self-enrichment scenario of globular clusters: the results from spectroscopic investigations of stars belonging to the second generation of clusters with different metallicity will be used as an indirect test of the reliability of the present yields. The treatment of mass loss and convection are confirmed as the main uncertainties affecting the results obtained in the context of the modeling of the thermal pulses phase. An indirect proof of this comes from the comparison with other investigations in the literature, based on a different prescription for the efficiency of convection in transporting energy and using a different recipe to determine the mass loss rate.