Two new Super Li-rich core He-burning giants: A new twist to the long tale of Li enhancement in K giants

TL;DR

This study reports two super Li-rich core He-burning giants, providing new insights into the recent Li enrichment processes during the RGB phase, which challenge existing models of stellar evolution.

Contribution

The paper identifies two new super Li-rich giants in the core He-burning phase, offering critical observational constraints on Li enrichment mechanisms in RGB stars.

Findings

Both stars are low-mass, Li-rich red clump giants.

Li enrichment likely occurred during He-flash or related events.

Findings challenge current models of Li production in giants.

Abstract

In this paper we report two new super Li-rich K giants: KIC 2305930 and KIC 12645107 with Li abundances exceeding that of ISM (A(Li) $\geq$ 3.2 dex). Importantly, both the giants have been classified as core He-burning red clump stars based on asteroseismic data from Kepler mission. Also, both the stars are found to be low mass (M $\approx$ 1.0 M$_{\odot}$) which, together with an evidence of their evolutionary status of being red clump imply that the stars have gone through both the luminosity bump and He-flash during their RGB evolution. Stars' large Li abundance and evolutionary phase suggest that Li enrichment occurred very recently probably at the tip of RGB either during He-flash, an immediate preceding event on RGB, or by some kind of external event such as merger of RGB star with white dwarf. The findings will provide critical constraints to theoretical models for understanding of Li enhancement origin in RGB stars.