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.

arXiv comment45 pages, 15 figures, 5 tables, PASJ in press (Already published online on February 22, 2015. doi:10.1093/pasj/psv001 )

References in corpus (39)

• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Kepler Mission Design, Realized Photometric Performance, and Early Science
• Kepler Input Catalog: Photometric Calibration and Stellar Classification
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• Rotation Periods of 34,030 Kepler Main-Sequence Stars: The Full Autocorrelation Sample
• Superflares on Solar Type Stars Observed with Kepler I. Statistical Properties of Superflares
• Global Energetics of Thirty-Eight Large Solar Eruptive Events
• The Effect of a Strong Stellar Flare on the Atmospheric Chemistry of an Earth-like Planet Orbiting an M dwarf
• Rotation and differential rotation of active Kepler stars
• A simple test for periodic signals in red noise
• Time scales of Li evolution: a homogeneous analysis of open clusters from ZAMS to late-MS
• Preparation of Kepler lightcurves for asteroseismic analyses
• A Revised Effective Temperature Scale for the Kepler Input Catalog
• Superflares on Ordinary Solar-Type Stars
• Rotation periods of 12 000 main-sequence Kepler stars: Dependence on stellar spectral type and comparison with v sin i observations
• Determining stellar macroturbulence using asteroseismic rotational velocities from Kepler
• Can Superflares Occur on Our Sun?
• Accurate parameters of 93 solar-type Kepler targets
• Stellar Parameters and Elemental Abundances of Late-G Giants
• The standard flare model in three dimensions. II. Upper limit on solar flare energy
• Superflares on Solar-Type Stars Observed with Kepler II. Photometric Variability of Superflare-Generating Stars : A Signature of Stellar Rotation and Starspots
• White-light flares on cool stars in the Kepler Quarter 1 Data
• A HR-like Diagram for Solar/Stellar Flares and Corona -- Emission Measure vs Temperature Diagram
• Measurements of Stellar Inclinations for Kepler Planet Candidates
• Superflare occurrence and energies on G-, K- and M-type dwarfs
• New measurements of rotation and differential rotation in A-F stars: Are there two populations of differentially rotating stars?
• Magnetic activity and differential rotation in the very young star KIC 8429280
• Measurements of Stellar Inclinations for Kepler Planet Candidates II: Candidate Spin-Orbit Misalignments in Single and Multiple-Transiting Systems
• Atmospheric parameters of 82 red giants in the Kepler field
• Behavior of Li abundances in solar-analog stars II. Evidence of the connection with rotation and stellar activity
• High-Dispersion Spectroscopic Study of Solar Twins: HIP 56948, HIP 79672, and HIP 100963
• Kepler super-flare stars: what are they?
• Two Sun-like Superflare Stars Rotating as Slow as the Sun
• The image slicer for the Subaru Telescope High Dispersion Spectrograph
• Keck/HIRES Spectroscopy of Four Candidate Solar Twins
• 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
• High Dispersion Spectroscopy of the Superflare Star KIC6934317
• Asteroseismology of Solar-type stars with Kepler III. Ground-based Data

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• Statistical Properties of Superflares on Solar-type Stars: Results Using All of the Kepler Primary Mission Data
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• Superflares on solar-type stars from the first year observation of TESS
• Impact of Stellar Superflares on Planetary Habitability
• Records of Sunspots and Aurora Candidates in the Chinese Official Histories of the Yuán and Míng Dynasties during 1261-1644
• High precision analysis of the solar twin HIP 100963
• A Great Space Weather Event in February 1730
• Spotting Stellar Activity Cycles in Gaia Astrometry
• Aurora Candidates from the Chronicle of Qīng Dynasty in Several Degrees of Relevance
• Starspot mapping with adaptive parallel tempering I: Implementation of computational code
• High Dispersion Spectroscopy of Solar-type Superflare Stars. III. Lithium Abundances
• Records of sunspot and aurora activity during 581-959 CE in Chinese official histories in the periods of Suí, Táng, and the Five Dynasties and Ten Kingdoms
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• Are Starspots and Plages Co-Located on Active G and K Stars?
• Characterization of Kepler targets based on medium-resolution LAMOST spectra analyzed with ROTFIT
• Starspots, chromospheric emission lines, and flares of zero-age main-sequence stars
• The Celestial Sign in the Anglo-Saxon Chronicle in the 770s: Insights on Contemporary Solar Activity
• Spectroscopic observations of flares and superflares on AU Mic
• Doppler imaging combined with high-cadence photometry. I. Revisiting the surface of a pre-main-sequence flare star
• High dispersion spectroscopy of solar-type superflare stars with Subaru/HDS