An Extremely Lithium-rich Bright Red Giant in the Globular Cluster M3

Abstract

We have serendipitously discovered an extremely lithium-rich star on the red giant branch of the globular cluster M3 (NGC 5272). An echelle spectrum obtained with the Keck I High-Resolution Echelle Spectrograph reveals a Li i l6707 resonance doublet of 520 mÅ equivalent width, and our analysis places the star among the most Li-rich giants known: . We determine the elemental abundances of this star, IV-101, and log e(Li) Ӎ ϩ3.0 three other cluster members of similar luminosity and color and conclude that IV-101 has abundance ratios typical of giants in M3 and M13 that have undergone significant mixing. We discuss mechanisms by which a low-mass star may be so enriched in Li, focusing on the mixing of material processed by the hydrogen-burning shell just below the convective envelope. While such enrichment could conceivably happen only rarely, it may in fact regularly occur during giant-branch evolution but be rarely detected because of rapid subsequent Li depletion.