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

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 Pᵣₒₜ=30.4±0.1~days, which translates to rotational velocity Vᵣₒₜ=19.5 ± 1.7~km s⁻¹. Star's location in the HR-diagram, derived values of ¹²C/¹³C = 7±1 and [C/N]=-0.95± 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 Vᵣₒₜ 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.