A Lithium-Rich Red Giant Below the Clump in the Kepler Cluster, NGC 6819

TL;DR

This study investigates lithium abundance patterns in NGC 6819's red giants, revealing a rare Li-rich star below the red giant bump and suggesting enhanced mixing processes.

Contribution

It provides new observational evidence of lithium distribution in an open cluster and identifies a Li-rich red giant below the bump, indicating possible non-standard mixing.

Findings

Most giants have low lithium levels below 1.0.

A Li-rich star with A(Li)=2.3 was identified below the red giant bump.

Li depletion pattern supports theories of mixing in stellar evolution.

Abstract

WIYN/HYDRA spectra in the Li 6708 Angstrom region have been obtained for 332 probable members of the old open cluster, NGC 6819. Preliminary analysis shows a pattern of Li depletion from the top of the turnoff to the base of the giant branch. Starting one magnitude below the level of the clump, all brighter giants have A(Li) below 1.0, with most having upper limits below 0.5. Star W007017, located BELOW the first-ascent red giant bump is Li-rich with A(Li) = 2.3. As a highly probable single-star astrometric and radial-velocity cluster member, its discrepant asteroseismic membership could be a by-product of the processes that triggered Li-enhancement. Its color-magnitude diagram location is consistent with only one proposed enhanced mixing process among first-ascent red giants.