High Dispersion Spectroscopy of Solar-type Superflare Stars. I. Temperature, Surface Gravity, Metallicity, and $v\sin i$

Abstract

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 ($T_{\mathrm{eff}}$), 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 ($(\Delta T_{\mathrm{eff}}{)}_{\mathrm{rms}}\sim 219$K, $(\Delta \log g{)}_{\mathrm{rms}}\sim 0.37$ dex, and $(\Delta [Fe/H]{)}_{\mathrm{rms}}\sim 0.46$ dex) are comparable to the large uncertainties and systematic differences of KIC values reported by the previous researches. We confirmed that the estimated $T_{\mathrm{eff}}$ 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 ($5600\le T_{\mathrm{eff}}\le 6000$K, $\log g\ge$4.0, and $P_0>$10 days). Five of the 34 target stars are fast rotators ($v\sin i\ge 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.

45 pages, 15 figures, 5 tables, PASJ in press (Already published online on February 22, 2015. doi:10.1093/pasj/psv001 )

References in corpus (5)

• Determining stellar macroturbulence using asteroseismic rotational velocities from Kepler
• Superflare occurrence and energies on G-, K- and M-type dwarfs
• Kepler super-flare stars: what are they?
• New solar twins and the metallicity and temperature scales of the Geneva Copenhagen Survey
• On detectability of Zeeman broadening in optical spectra of F- and G-dwarfs

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