High dispersion spectroscopy of solar-type superflare stars. I. Temperature, surface gravity, metallicity, and vsin i

• Published in: Publications of the Astronomical Society of Japan 2015-06, Vol.67 (3)
• Main Authors: Notsu, Yuta, Honda, Satoshi, Maehara, Hiroyuki, Notsu, Shota, Shibayama, Takuya, Nogami, Daisaku, Shibata, Kazunari
• Format: Article
• Language: English
• ISSN: 0004-6264
• DOI: 10.1093/pasj/psv001

We conducted high-dispersion spectroscopic observations of 50 superflare stars with Subaru High Dispersion Spectrograph (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) of our 50 targets have no evidence of binary systems. We then estimated the effective temperature (T eff), surface gravity (log g), metallicity ([Fe/H]), and projected rotational velocity (vsin i) of these 34 superflare stars on the basis of our spectroscopic data. The accuracy of our estimations is higher than that of the Kepler Input Catalog (KIC) values, and the differences between our values and KIC values [(ΔT eff)rms ∼ 219 K, (Δlog g)rms ∼ 0.37 dex, and (Δ[Fe/H])rms ∼ 0.46 dex] are comparable to the large uncertainties and systematic differences of KIC values reported by the previous researchers. 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 nine of the stars are in the range of “Sun-like” stars (5600 ≤ T eff ≤ 6000 K, log g ≥ 4.0, and P 0 > 10 d). Five of the 34 target stars are fast rotators (vsin i ≥ 10 km s−1), while 22 stars have relatively low vsin i values (vsin i