KIC 9821622: An interesting lithium-rich giant in the Kepler field

TL;DR

This paper reports the discovery and detailed analysis of KIC 9821622, a young, lithium-rich giant star with unusual elemental enhancements, providing insights into stellar evolution and nucleosynthesis processes.

Contribution

It presents the first detailed chemical and evolutionary analysis of a lithium-rich giant with unusual elemental enhancements, combining spectroscopic and asteroseismic data.

Findings

KIC 9821622 is a Li-rich giant near the luminosity bump.

It shows elevated Fe-peak and r-process element abundances.

The star is young, about 2.37 Gyr, with high alpha-element levels.

Abstract

We report the discovery of a new exceptional young lithium-rich giant, KIC 9821622, in the \textit{Kepler} field that exhibits an unusually large enhancement of $\alpha$, Fe-peak, and \textit{r}-process elements. From high-resolution spectra obtained with GRACES at Gemini North, we derived fundamental parameters and detailed chemical abundances of 23 elements from equivalent widths and synthesis analysis. By combining atmospheric stellar parameters with available asteroseismic data, we obtained the stellar mass, radius, and age. The data analysis reveals that KIC 9821622 is a Li-rich (A(Li)$_{NLTE}$ = 1.80 $\pm$ 0.2) intermediate-mass giant star ($M$ = 1.64 $M_{\odot}$) located at the red giant branch near the luminosity bump. We find unexpectedly elevated abundances of Fe-peak and \textit{r}-process elements. In addition, as previously reported, we find that this is a young star (2.37 Gyr) with unusually high abundances of $\alpha$-elements ([$\alpha$/Fe] = 0.31). The evolutionary status of KIC 9821622 suggests that its Li-rich nature is the result of internal fresh Li that is synthesized through the Cameron-Fowler mechanism near the luminosity bump. However, its peculiar enhancement of $\alpha$, Fe-peak, and \textit{r}-process elements opens the possibility of external contamination by material enriched by a supernova explosion. Although it is less likely, planet accretion cannot be ruled out.