We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS , and measured the stellar parameters of them .
These 50 targets were selected from the solar-type ( G-type main sequence ) superflare stars that we had discovered from the Kepler photometric data .
As a result of these spectroscopic observations , we found that more than half ( 34 stars ) of our 50 targets have no evidence of binary system .
We then estimated effective temperature ( T _ { eff } ) , surface gravity ( \log g ) , metallicity ( [ Fe/H ] ) , and projected rotational velocity ( v \sin i ) of these 34 superflare stars on the basis of our spectroscopic data .
The accuracy of our estimations is higher than that of Kepler Input Catalog ( KIC ) values , and the differences between our values and KIC values ( ( \Delta T _ { eff } ) _ { rms } \sim 219 K , ( \Delta \log g ) _ { rms } \sim 0.37 dex , and ( \Delta [ Fe / H ] ) _ { rms } \sim 0.46 dex ) are comparable to the large uncertainties and systematic differences of KIC values reported by the previous researches .
We confirmed that the estimated T _ { eff } and \log g values of the 34 superflare stars are roughly in the range of solar-type stars .
In particular , these parameters and the brightness variation period ( P _ { 0 } ) of 9 stars are in the range of “ Sun-like ” stars ( 5600 \leq T _ { eff } \leq 6000 K , \log g \geq 4.0 , and P _ { 0 } > 10 days ) .
Five of the 34 target stars are fast rotators ( v \sin i \geq 10 km s ^ { -1 } ) , while 22 stars have relatively low v \sin i values ( v \sin i < 5 km s ^ { -1 } ) .
These results suggest that stars whose spectroscopic properties similar to the Sun can have superflares , and this supports the hypothesis that the Sun might cause a superflare .