(Proposal ID) S12B-111

(PI) Notsu, Yuta

(Proposal Title)
High Dispersion Spectroscopy of Solar-Type Stars showing Superflares

(Abstract)
We propose high dispersion spectroscopy of solar-type stars (G-type main 
sequence stars) which can show "superflares". Our detailed analysis of the 
Kepler data claims that superflares can occur  on slowly rotating Sun-like 
stars, and superflare-generating stars have large starspots. However, the 
detailed properties and mechanism are not clear. We investigate changes of 
lines profile caused by the rotation of the star with starspots, by high 
dispersion spectroscopy with HDS. We focus on Ca II IR triplet, and H alpha, 
since these absorption. Such absorption lines are sensitive to chromospheric 
activity of active region including starspots. We also measure v sin i, and 
estimate the inclination angle by comparing v sin i with the rotation speed 
evaluated from the period of the brightness variations. Modeling of the 
brightness variations, using the accurate inclination angle, will enables us 
to clarify the size and position of the starspot, and the differential 
rotation. Third, we aim to measure radial velocity (RV) changes between the 
observations and to investigate the binary fraction of solar-type stars 
showing  superflares. This study will lead to the understanding the mechanism 
of superflares and can be useful for many fields such as solar/stellar physics 
and astrobiology.