(Proposal ID) S13A-045

(PI) Notsu, Yuta

(Proposal Title)
High Dispersion Spectroscopy of Sun-like Stars showing Superflares

(Abstract)
We propose high dispersion spectroscopy of Sun-like "superflare" stars  to 
investigate whether our Sun has superflares.  Our detailed analysis of the 
Kepler data claims that superflares can occur on solar-type (G-type main 
sequence) stars exhibiting brightness modulations with a long period, P>10 d, 
and superflare stars have large starspots. However, the detailed properties of 
these stars  and mechanism of superflares are not clear. We have three main 
purposes.  First, we measure the line profile of Ca II IR triplet and H alpha. 
These absorption lines are sensitive to chromospheric activity  of active 
regions including starspots.  Second, we measure v sin i, and confirm  that 
the target stars really slowly rotate like the Sun. Third, we aim to check 
whether the targets are a visual or spectroscopic binary. We also measure 
radial velocity (RV) changes between the observations separated by several 
days (>3 days).  We investigate the binary fraction of solar-type stars 
showing superflares.  This study will lead to understanding the mechanism of 
superflares and is very important for solar/stellar physics.