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

摘要

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 ~(6) Li ( & 3%), a low carbon isotopic ratio ( ~(12) C/ ~(13) C = 12 ± 2 ), and the slow rotation ( v sin 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 ~(7) Li synthesis in HD 16771 is triggered by the engulfment of close-in planet(s) during the RGB phase.