Survey of Li-rich giants among Kepler and LAMOST fields: determination of Li-rich giants' evolutionary phase

Abstract

In this Letter, we report the discovery of 24 new super Li-rich (A(Li) ≥ 3.2) giants of He-core burning phase at the red clump region. Results are based on a systematic search of a large sample of about 12,500 giants common to the LAMOST spectroscopic and Kepler time-resolved photometric surveys. The two key parameters derived from Kepler data are an average period spacing (Δp) between l = 1 mixed gravity-dominated g-modes and average large frequency-separation (Δν) l = 0 acoustic p-modes, which suggest all the Li-rich giants are in the He-core burning phase. This is the first unbiased survey subjected to a robust technique of asteroseismic analysis to unambiguously determine the evolutionary phase of Li-rich giants. The results provide strong evidence that the Li enhancement phenomenon is associated with giants in the He-core burning phase post He-flash, rather than any other phase on the red giant branch with an inert He-core surrounded by a H-burning shell.