HD 16771: A lithium-rich giant in the red-clump stage

Abstract

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 ∈ (Li) = + 2.67 ± 0.10 dex) intermediate mass giant star (M = 2.4 ± 0.1 M⊙) with age ∼ 0.76 ± 0.13 Gyr 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-1) all suggest that lithium might have been synthesized in this star. On the contrary, HD 16771 with a mass of 2.4 M⊙ 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.