Most Lithium-rich Low-mass Evolved Stars Revealed as Red Clump stars by Asteroseismology and Spectroscopy

TL;DR

This study uses asteroseismology and spectroscopy to show that most lithium-rich low-mass evolved stars are red clump stars, revealing new insights into their chemical compositions and evolutionary states.

Contribution

It provides the first large systematic analysis combining asteroseismology and spectroscopy to classify lithium-rich stars, showing most are red clump stars rather than RGB.

Findings

Most lithium-rich stars are confirmed to be red clump stars.

Lithium abundance distribution differs significantly between RC and RGB stars.

Li abundances in RCs extend to higher values than in RGBs.

Abstract

Lithium has confused scientists for decades at almost each scale of the universe. Lithium-rich giants are peculiar stars with lithium abundances over model prediction. A large fraction of lithium-rich low-mass evolved stars are traditionally supposed to be red giant branch (RGB) stars. Recent studies, however, report that red clump (RC) stars are more frequent than RGB. Here, we present a uniquely large systematic study combining the direct asteroseismic analysis with the spectroscopy on the lithium-rich stars. The majority of lithium-rich stars are confirmed to be RCs, whereas RGBs are minor. We reveal that the distribution of lithium-rich RGBs steeply decline with the increasing lithium abundance, showing an upper limit around 2.6 dex, whereas the Li abundances of RCs extend to much higher values. We also find that the distributions of mass and nitrogen abundance are notably different between RC and RGB stars. These findings indicate that there is still unknown process that significantly affects surface chemical composition in low-mass stellar evolution.