2014A&A...564L...6M

The existence of lithium-rich low-mass red giant stars still represents a challenge for stellar evolution models. Stellar clusters are privileged environments for this kind of investigation. To investigate the chemical abundance pattern of the old open cluster Trumpler5, we observed a sample of four red-clump stars with high-resolution optical spectrographs. One of them (#3416) reveals extremely strong lithium lines in its spectrum. One-dimensional, local thermodynamic equilibrium analysis was performed on the spectra of the observed stars. A 3D-NLTE analysis was performed to derive the lithium abundance of star #3416. Star #3416 is super Li-rich with A(Li)=3.75dex. The lack of ⁶Li enrichment (⁶Li/⁷Li<2%), the low carbon isotopic ratio (¹²C/¹³C=14±3), and the lack of evidence for radial velocity variation or enhanced rotational velocity (vsini=2.8km/s) all suggest that lithium production has occurred in this star through the Cameron & Fowler (1971ApJ...164..111C) mechanism. We identified a super Li-rich core helium-burning, red-clump star in an open cluster. Internal production is the most likely cause of the observed enrichment. Given the expected short duration of a star's Li-rich phase, enrichment is likely to have occurred at the red clump or in the immediately preceding phases, namely during the He-flash at the tip of the red giant branch (RGB) or while ascending the brightest portion of the RGB.