High Dispersion Spectroscopy of Solar-type Superflare Stars. III. Lithium Abundances

TL;DR

This study analyzes lithium abundances in solar-type superflare stars using high-resolution spectroscopy to understand their ages, rotational properties, and potential Li production by superflares, revealing a wide age range and no evidence of Li synthesis during superflares.

Contribution

First detailed Li abundance analysis of superflare stars, linking stellar age, rotation, and flare activity, with implications for stellar evolution and nucleosynthesis.

Findings

Large dispersion in Li abundances among superflare stars

Some stars are younger than Hyades cluster, others are older like the Sun

No evidence found for Li production by superflares

Abstract

We report on the abundance analysis of Li in solar-type (G-type main sequence) superflare stars which were found by the analysis of Kepler photometric data. Li is a key element to understand the evolution of the stellar convection zone which reflects the age of solar-type stars. We performed the high dispersion spectroscopy of solar-type superflare stars with Subaru/HDS, and confirmed that 34 stars show no evidence of binarity in our previous study. In this study, we derived the Li abundances of these 34 objects. We investigate correlations of Li abundance with stellar atmospheric parameters, rotational velocity, and superflare activities to understand the nature of superflare stars and the possibility of the nucleosynthesis of Li by superflares. We confirm the large dispersion in the Li abundance, and the correlation with stellar parameters is not seen. As compared with the Li abundance in Hyades cluster which is younger than the Sun, it is suggested that half of the observed stars are younger than Hyades cluster. The measured value of $v \sin i$ (projected rotational velocity) supports those objects are younger than the Sun. However, there are some objects which show the low Li abundance and slowly rotate on the basis of the estimated $v \sin i$ and $P$ (period of brightness variation). This result indicates that the superflare stars are not only young stars but also old stars like our Sun. In our observations, we could not find any evidence of Li productions by superflares. Further research on Li isotope abundances of superflare stars would clarify the Li production by stellar flares.