The Abundance of Lithium in an AGB Star in the Globular Cluster M3 (NGC 5272)

TL;DR

This study reports the detection of a lithium-rich asymptotic giant branch star in globular cluster M3, confirming its lithium abundance and suggesting internal production via the Cameron-Fowler mechanism.

Contribution

First identification of a lithium-rich AGB star in M3 with detailed spectroscopic analysis and implications for lithium production in globular cluster stars.

Findings

Detected high lithium abundance in vZ 1050

Confirmed vZ 1050 as a first-generation star

Suggested lithium enhancement via internal mechanisms

Abstract

A survey of red giants in the globular cluster M3 with the Hydra multi-object spectrograph on the WIYN 3.5-m telescope indicated a prominent Li I 6707 $\AA$ feature in the red giant vZ 1050. Follow-up spectroscopy with the ARC 3.5-m telescope confirmed this observation and yielded a derived abundance of A(Li)$_{NLTE}$ = 1.6 $\pm$ 0.05. In addition, the high oxygen and low sodium abundances measured from the same spectrum suggest that vZ 1050 is a first generation cluster star. The location vZ 1050 above the horizontal branch and blueward of the red giant branch in the cluster's color-magnitude diagram places vZ 1050 on M3's asymptotic giant branch. The likely source for the enhanced lithium abundance is the Cameron-Fowler mechanism operating in vZ 1050 itself.