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

W.J. McDonald Observatory and Department of Astronomy, The University of Texas at Austin, Austin, TX 78712-1205, USA
e-mail: bala@astro.as.utexas.edu

Received: 16 February 2016
Accepted: 15 March 2016

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 ϵ(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.