2016A&A...589A..57R

Aims. We report the discovery of a young lithium rich giant, HD 16771, in the core-helium burning phase that does not seem to fit existing proposals of Li synthesis near the luminosity function bump or during He-core flash. We aim to understand the nature of Li enrichment in the atmosphere of HD 16771 by exploring various Li enhancement scenarios.
Methods. We have collected high-resolution echelle spectra of HD 16771 and derived stellar parameters and chemical abundances for 27 elements by either line equivalent widths or synthetic spectrum analyses.
Results. HD 16771 is a Li-rich (log ε(Li)=+ 2.67±0.10dex) intermediate mass giant star (M=2.4±0.1M_☉) with age∼0.76±0.13Gyr and located at the red giant clump. Kinematics and chemical compositions are consistent with HD 16771 being a member of the Galactic thin disk population. The non-detection of ⁶Li (<3%), a low carbon isotopic ratio (¹²C/¹³C=12±2), and the slow rotation (vsin i=2.8 km/s) all suggest that lithium might have been synthesized in this star. On the contrary, HD 16771 with a mass of 2.4M_☉ has no chance of encountering luminosity function bump and He-core flash where the possibility of fast deep-mixing for Li enrichment in K giants has been suggested previously.
Conclusions. Based of the evolutionary status of this star, we discuss the possibility that ⁷Li synthesis in HD 16771 is triggered by the engulfment of close-in planet(s) during the RGB phase.