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

TL;DR

This paper reports the discovery of a lithium-rich giant star, HD 16771, in the red-clump phase, exploring its unusual lithium enrichment and suggesting planet engulfment as a possible cause.

Contribution

It presents detailed chemical and kinematic analysis of HD 16771, a rare lithium-rich giant in the red-clump stage, challenging existing lithium synthesis theories.

Findings

HD 16771 is a lithium-rich giant with log(n(Li))=+2.67.

The star's properties suggest lithium synthesis possibly due to planet engulfment.

The star's evolutionary status excludes common lithium enrichment scenarios.

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(n(Li))=+2.67+/-0.10 dex) intermediate mass giant star (M=2.4+/-0.1 Msun) 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 (vsini=2.8 km/s) all suggest that lithium might have been synthesized in this star. On the contrary, HD 16771 with a mass of 2.4 Msun 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.