Study of a red clump giant, KIC~11087027, with high rotation and strong infrared excess -- Evidence of tidal interaction for high lithium abundance

TL;DR

This study investigates a super Li-rich red clump giant star with high rotation and infrared excess, providing evidence of tidal interaction possibly linked to recent He-flash events and binary interaction.

Contribution

It presents detailed photometric and spectroscopic analysis of KIC 11087027, revealing its high rotation, lithium enrichment, and binary nature, suggesting tidal synchronization influences lithium dredge-up.

Findings

Star's rotational period is 30.4 days with V_rot=19.5 km/s.

Star shows high lithium abundance and infrared excess.

Evidence suggests recent He-flash and binary interaction influence star's properties.

Abstract

This paper presents results from Kepler photometric light curves and high-resolution spectroscopic study of a super Li-rich giant KIC11087027. Using the light curve analysis, we measured the star's rotational period P$_{\rm rot}$=30.4$\pm$0.1~days, which translates to rotational velocity V$_{\rm rot}$=19.5 $\pm$ 1.7~km s$^{-1}$. Star's location in the HR-diagram, derived values of $^{12}C/^{13}C$ = 7$\pm$1 and $[C/N]=-0.95\pm 0.2$, and the inferred asteroseismic parameters from secondary calibration based on spectra suggest star is a low-mass red clump giant in the He-core burning phase. Using Gaia data, we found evidence of variation in radial velocity and proper motion, indicative of presence of an unresolved binary. The large V$_{\rm rot}$ is probably a result of tidal synchronization combined with the after-effects of He-flash, in which the size of the star is reduced significantly. The simultaneous presence of features like high rotation, very high Li abundance, strong dust shell, and strong flares in a single star is relatively uncommon, suggesting that the star experiencing tidal synchronization has recently undergone He-flash. The results pose a question whether the binary interaction, hence the high rotation, is a prerequisite for dredging-up of the high amounts of Li from the interior to the photosphere during or immediately after the He-flash event.