Study of Lithium-rich giants with the GALAH spectroscopic survey

Abstract

In this article, we speculate on the possible mechanisms for Li enhancement origin in RGB stars based on a large data set of around 340 299 stars collected from the GALAH survey combined with the Gaia astrometry. Data has 51 982 low mass (M ≤ 2 M⊙) RGB stars with reliable atmospheric parameters. The data set shows a well-populated RGB with well-defined luminosity bump and red clump with significant number of stars at each of these two key phases. We found 335 new Li-rich RGB stars with Li abundance, A(Li) ≥ 1.80 ± 0.14 dex, of which 20 are super Li-rich with A(Li) ≥ 3.20 dex. Most of them appear to be in the red clump region which, when combined with stellar evolutionary time-scales on RGB, indicates that the Li enhancement origin may lie at RGB tip during He-flash rather than by external source of merging of sub-stellar objects or during luminosity bump evolution. Kinematic properties of sample stars suggest that Li-rich giants are relatively more prevalent among giants of thin disc compared to thick disc and halo.