Lithium abundances in red giants of M4: evidence for asymptotic giant branch star pollution in globular clusters?

TL;DR

This study measures lithium abundances in M4 globular cluster giants, providing evidence that asymptotic giant branch stars contributed to cluster pollution, supporting multiple population formation scenarios.

Contribution

It presents Li abundance data for M4 giants, showing evidence of Li production and supporting the role of AGB stars in globular cluster pollution.

Findings

First and second generation stars share the same Li content

Evidence of Li production in the cluster

Supports AGB stars as polluters in GCs

Abstract

The determination of Li and proton-capture element abundances in globular cluster (GC) giants allows us to constrain several key questions on the multiple population scenarios in GCs, from formation and early evolution, to pollution and dilution mechanisms. In this Letter, we present our results on Li abundances for a large sample of giants in the intermediate-metallicity GC NGC 6121 (M4), for which Na and O have been already determined by Marino et al. The stars analyzed are both below and above the red giant branch bump luminosity. We found that the first and second generation stars share the same Li content, suggesting that a Li production must have occurred. This is a strong observational evidence providing support for the scenario in which asymptotic giant branch stars are GC polluters.