Evolution of long-lived globular cluster stars. II. Sodium abundance variations on the asymptotic giant branch as a function of globular cluster age and metallicity

TL;DR

This study examines how age and metallicity influence sodium abundance variations among asymptotic giant branch stars in globular clusters, providing insights into their self-enrichment history and stellar evolution.

Contribution

It offers a theoretical analysis of sodium abundance variations on the AGB as a function of cluster age and metallicity within the fast rotating massive stars scenario.

Findings

Na abundance variations depend on cluster age and metallicity

The ratio of Na-poor to Na-rich stars varies with cluster properties

Results support self-enrichment models involving massive star pollution

Abstract

Long-lived stars in GCs exhibit chemical peculiarities with respect to their halo counterparts. In particular, Na-enriched stars are identified as belonging to a 2d stellar population born from cluster material contaminated by the H-burning ashes of a 1st stellar population. Their presence and numbers in different locations of the CMDs provide important constraints on the self-enrichment scenarios. In particular, the ratio of Na-poor to Na-rich stars on the AGB has recently been found to vary strongly from cluster to cluster, while it is relatively constant on the RGB. We investigate the impact of both age and metallicity on the theoretical Na spread along the AGB within the framework of the fast rotating massive stars scenario for GC self-enrichment. (tb continued)