High dispersion spectroscopy of solar-type superflare stars with Subaru/HDS

TL;DR

This study used Subaru/HDS spectroscopy to analyze 50 solar-type superflare stars from Kepler data, confirming their stellar parameters and linking brightness variations to large starspots and chromospheric activity.

Contribution

It provides detailed spectroscopic analysis of superflare stars, confirming the connection between brightness variation, starspots, and chromospheric activity, and clarifies their stellar properties.

Findings

Most stars are single and solar-like in parameters.

Rotational velocity matches brightness variation estimates.

Large brightness variations correlate with high chromospheric activity.

Abstract

We carried out spectroscopic observations with Subaru/HDS of 50 solar-type superflare stars found from Kepler data. More than half (34 stars) of the target stars show no evidence of the binary system, and we confirmed atmospheric parameters of these stars are roughly in the range of solar-type stars. We then conducted the detailed analyses for these 34 stars. First, the value of the "$v\sin i$" (projected rotational velocity) measured from spectroscopic results is consistent with the rotational velocity estimated from the brightness variation. Second, there is a correlation between the amplitude of the brightness variation and the intensity of Ca II IR triplet line. All the targets expected to have large starspots because of their large amplitude of the brightness variation show high chromospheric activities compared with the Sun. These results support that the brightness variation of superflare stars is explained by the rotation of a star with large starspots.