The Gaia-ESO Survey: an extremely Li-rich giant in the globular cluster NGC 1261

TL;DR

This paper reports the discovery of the first lithium-rich giant star in the globular cluster NGC 1261, highlighting its extreme Li overabundance and discussing potential production mechanisms.

Contribution

It presents the first identification of a Li-rich giant in NGC 1261 and analyzes its properties, suggesting possible origins like extra mixing or binary mass transfer.

Findings

Extreme Li overabundance detected in the star

Possible Li production via extra mixing or binary transfer

Low barium abundance supports binary transfer hypothesis

Abstract

Lithium rich stars in globular clusters are rare. In fact, only 14 have been found so far, in different evolutionary phases from dwarfs to giants. Different mechanisms have been proposed to explain this enhancement, but it is still an open problem. Using spectra collected within the Gaia-ESO Survey, obtained with the GIRAFFE spectrograph at the ESO Very Large Telescope, we present the discovery of the first Li-rich star in the cluster NGC 1261, the second star known in the red giant branch bump phase. The star shows an extreme Li overabundance of A(Li)_LTE=3.92\pm0.14, corresponding to A(Li)_NLTE=3.40 dex. We propose that the Li enhancement is caused by fresh Li production through an extra mixing process (sometimes referred to as {\em cool bottom burning}) or could be a pre-existing Li overabundance resulting from binary mass transfer, likely from a red giant branch star, because of the low barium abundance. To unambiguously explain the Li enhancement in globular cluster stars, however, a reliable determination of the abundance of key species like Be, 6Li, 12C/13C, and several s-process elements is required, as well as detailed modeling of chromospheric activity indicators.