Self-enrichment by AGB stars in Globular Clusters: comparison between intermediate and high metallicities

TL;DR

This study models intermediate-mass AGB stars at high metallicity to evaluate their role in globular cluster self-enrichment, finding that yields and abundance patterns are affected by metallicity but still support the self-enrichment scenario.

Contribution

It provides new theoretical evolutionary sequences for AGB stars at high metallicity and compares their yields to those at intermediate metallicity, assessing implications for globular cluster chemical evolution.

Findings

Higher metallicity slightly decreases luminosity and temperature at the envelope base.

Yields are affected by metallicity, altering abundance relationships.

Models align with observed element anticorrelations if stars >5 solar masses contribute.

Abstract

We present theoretical evolutionary sequences of intermediate mass stars (M=3-6.5 solar masses) with metallicity Z=0.004. Our goal is to test whether the self-enrichment scenario by massive Asymptotic Giant Branch stars may work for the high metallicity Globular Clusters, after previous works by the same group showed that the theoretical yields by this class of objects can reproduce the observed trends among the abundances of some elements, namely the O-Al and O-Na anticorrelations, at intermediate metallicities, i.e [Fe/H]=-1.3. We find that the increase in the metallicity favours only a modest decrease of the luminosity and the temperature at the bottom of the envelope for the same core mass, and also the efficiency of the third dredge-up is scarcely altered. On the contrary, differences are found in the yields, due to the different impact that processes with the same efficiency have on the overall abundance of envelopes with different metallicities. We expect the same qualitative patterns as in the intermediate metallicity case, but the slopes of some of the relationships among the abundances of some elements are different. We compare the sodium-oxygen anticorrelation for clusters of intermediate metallicity (Z~0.001) and clusters of metallicity large as in these new models. Although the observational data are still too scarce, the models are consistent with the observed trends, provided that only stars of M>5 solar masses contribute to self-enrichment.