High Dispersion Spectroscopy of Solar-type Superflare Stars. II. Stellar Rotation, Starspots, and Chromospheric Activities

Abstract

We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS. These 50 stars were selected from the solar-type superflare stars that we had discovered from the Kepler data. More than half (34 stars) of these 50 target superflare stars show no evidence of binarity, and we estimated stellar parameters of these 34 stars in our previous study (Notsu et al. 2015, hereafter called Paper I). According to our previous studies using Kepler data, superflare stars show quasi-periodic brightness variations whose amplitude (0.1-10\%) is much larger than that of the solar brightness variations (0.01-0.1\%) caused by the existence of sunspots on the rotating solar surface. In this study, we investigated whether these quasi-periodic brightness variations of superflare stars are explained by the rotation of a star with fairly large starspots, by using stellar parameters derived in Paper I. First, we confirmed that the value of the projected rotational velocity $v\sin i$ is consistent with the rotational velocity estimated from the period of the brightness variation. Next, we measured the intensity of Ca II infrared triplet lines and H$\alpha$ line, good indicators of the stellar chromospheric activity, and compared them with other stellar properties. The intensity of Ca II infrared triplet lines indicates that the mean magnetic field strength ($⟨fB⟩$) of the target superflare stars can be higher than that of the Sun. A correlation between the amplitude of the brightness variation and the intensity of Ca II triplet line was found. All the targets expected to have large starspots because of their large amplitude of the brightness variation show high chromospheric activities compared to the Sun. These results support that the brightness variation of superflare stars is due to the rotation with large starspots.

arXiv comment25 pages, 9 figures, 1 tables, accepted for publication in PASJ

References in corpus (18)

• Kepler Mission Design, Realized Photometric Performance, and Early Science
• Kepler Input Catalog: Photometric Calibration and Stellar Classification
• Superflares on Solar Type Stars Observed with Kepler I. Statistical Properties of Superflares
• Global Energetics of Thirty-Eight Large Solar Eruptive Events
• Rotation and differential rotation of active Kepler stars
• Time scales of Li evolution: a homogeneous analysis of open clusters from ZAMS to late-MS
• Superflares on Ordinary Solar-Type Stars
• Can Superflares Occur on Our Sun?
• Photometric Variability in Kepler Target Stars. II. An Overview of Amplitude, Periodicity, and Rotation in First Quarter Data
• Superflares on Solar-Type Stars Observed with Kepler II. Photometric Variability of Superflare-Generating Stars : A Signature of Stellar Rotation and Starspots
• Sun-as-a-Star Spectrum Variations 1974-2006
• Measurements of Stellar Inclinations for Kepler Planet Candidates
• Magnetic activity and differential rotation in the very young star KIC 8429280
• The effect of magnetic activity saturation in chromospheric flux-flux relationships
• Behavior of Li abundances in solar-analog stars II. Evidence of the connection with rotation and stellar activity
• Two Sun-like Superflare Stars Rotating as Slow as the Sun
• On detectability of Zeeman broadening in optical spectra of F- and G-dwarfs
• High Dispersion Spectroscopy of the Superflare Star KIC6934317

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