著者

野津 湧太 前原 裕之 行方 宏介 野津 翔太 幾田 佳 本田 敏志 野上 大作 柴田 一成

出版者

日本地球惑星科学連合

雑誌

JpGU-AGU Joint Meeting 2017

巻号頁・発行日

2017-03-10

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Flares on G, K, M-type stars are sudden releases of the magnetic energy stored around the starspots, like solar flares. Recent high-precision photometry from space shows that "superflares", which are 10-104 times more energetic than the largest solar flares, occur on many G, K, M-type stars including Sun-like stars (slowly-rotating G-type main-sequence stars like the Sun) (e.g., Maehara et al. 2012 Nature). Such superflares emit harmful UV/X-ray radiation and high-energy particles such as protons, and may suggest that exoplanet host stars have severe effects on the physical and chemical evolution of exoplanetary atmospheres (cf. Segura et al. 2010 Astrobiology, Takahashi et al. 2016 ApJL). It is then important to know the detailed properties of such superflare events for considering the habitability of planets.In this presentation, we present statistical properties of superflares on G, K, M-type stars on the basis of our analyses of Kepler photometric data (cf. Maehara et al. 2012 Nature, Shibayama et al. 2013 ApJS, Notsu et al. 2013 ApJ, Maehara et al. 2015 EPS). We found more than 5000 superflares on 800 G, K, M-type main-sequence stars, and the occurrence frequency (dN/dE) of superflares as a function of flare energy (E) shows the power-law distribution with the power-law index of -1.8~-1.9. This power-law distribution is consistent with that of solar flares.Flare frequency increases as stellar temperature decreases. As for M-type stars, energy of the largest flares is smaller (~1035 erg) compared with G,K-type stars, but more frequent "hazardous" flares for the habitable planets since the habitable zone around M-type stars is much smaller compared with G, K-types stars.Flare frequency has a correlation with rotation period, and this suggests young rapidly-rotating stars (like "young Sun") have more severe impacts of flares on the planetary atmosphere (cf. Airapetian et al. 2016 Nature Geoscience). Maximum energy of flares and flare frequency also depends on the area of starspots, and this suggest existence of large starspots is important factor of superflares.The statistical properties of superflares discussed here can be one of the basic information for considering the impacts of flares on planet-host stars.

著者

本田 敏志 定金 晃三 田鍋 和仁

出版者

大阪教育大学

雑誌

大阪教育大学紀要 3 自然科学・応用科学 (ISSN:13457209)

巻号頁・発行日

vol.46, no.2, pp.219-229, 1998-01

被引用文献数

1

著者

前原 裕之 野津 湧太 野津 翔太 行方 宏介 本田 敏志 石井 貴子 野上 大作 柴田 一成

出版者

日本地球惑星科学連合

雑誌

JpGU-AGU Joint Meeting 2017

巻号頁・発行日

2017-03-10

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Recent space-based observations (e.g., Kepler mission) enable us to investigate the nature of “superflares” on solar-type stars (G-type main sequence stars). The bolometric energy of superflares ranges from 1033 erg to 1036 erg which is 10-104 times larger than that released by a typical X10 class solar flare. Most of the stars with superflares show large-amplitude photometric variations associated with the stellar rotation which suggest that the stars with superflares have large starspots. Spectroscopic studies of superflare stars revealed that the chromospheric activity correlates with the amplitude of brightness variations.We analyze the correlation between starspots and superflares on solar-type stars using the data from the Kepler mission. Our analysis shows that the fraction of the stars showing superflares decreases as the rotation period increases and as the amplitude of photometric variations, which is thought to correlate with the area of starspots, decreases. We found that the fraction of superflare stars among the stars with large starspots also decreases as the rotation period increases. This suggests that some of the slowly-rotating stars with large starspots show a much lower flare activity than the superflare stars with the same spot area and rotation period.Assuming simple relations between spot area and life time and between spot temperature and photospheric temperature, we compared the size distribution of large starspots with the area of >104 MSH (micro solar hemispheres; 1 MSH=3x1016 cm2) on slowly-rotating solar-type stars with that of sunspot groups. The size distribution of starspots shows the power-law distribution and that of larger sunspots lies on the same power-law line. The size distribution of spots from the Kepler data suggests that the average appearance frequency of the starspots with the area of >3x104 MSH on the solar-type stars with the rotation period similar to that of the Sun is once in a few hundred years.We also found that the frequency-energy distributions for flares originating from spots with different sizes are the same for solar-type stars with superflares and the Sun. These results suggest that the magnetic activity on solar-type stars with superflares and that on the Sun is caused by the same physical processes.

著者

高橋 隼 浦川 聖太郎 寺居 剛 花山 秀和 新井 彰 本田 敏志 高木 悠平 伊藤 洋一

出版者

日本惑星科学会

雑誌

日本惑星科学会秋期講演会予稿集

巻号頁・発行日

vol.2013, pp."P2-04", 2013-11-20

著者

橋本 修 高橋 英則 本田 敏志 田口 光 衣笠 健三

出版者

群馬県立ぐんま天文台

雑誌

基盤研究(C)

巻号頁・発行日

2007

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恒星進化末期の漸近巨星枝(AGB)にある炭素星の形成とその進化シナリオを検討するため、炭素星の可視高分散分光観測を行い、炭素の同位体比^<12>C/^<13>Cを測定する。ぐんま天文台のGAOES分光器を用いることによって、高い波長分解能でありながら、かつ広い波長領域を網羅した高精度の可視分光データを大量のサンプルに対して取得した。この様な大型サンプルに対する高精度の炭素同位体比の測定はこれまでに類をみないものである。

著者

定金 晃三 横尾 武夫 福江 純 松本 桂 有本 淳一 小林 英之 本田 敏志

出版者

大阪教育大学

雑誌

大阪教育大学紀要. 第III部門, 自然科学・応用科学 (ISSN:13457209)

巻号頁・発行日

vol.44, no.1, pp.55-65, 1995-09

被引用文献数

1

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大阪教育大学に設置された口径50cm の反射望遠鏡には,観測装置として液体窒素冷却の高性能CCDカメラが備えられている。さまざまな種類の天体観測を行いながら,このCCDカメラそのものの性能の評価と柏原キャンパスにおける天体観測性能の評価を行った。結果として,CCDカメラの冷却性能,読み出しノイズのレベル,直線性などはいずれも良好であることがわかった。空の明るさの計測を行った結果,柏原の空は市街光の影響を著しく受けており,しかも,方向によって影響の大きさが異なることが分かった。多数のイメージを計測した結果,星像の大きさの平均は現状ではおよそ4秒角である。点光源(星)を対象とした場合,120秒間の露出を4ないし5回行うことで14等台の明るさの天体の相対測光観測が0.02等の精度で行えることがわかった。We have conducted an extensive series of tests of the CCD camera which is used at the Cassegrain focus of the 50 cm telescope of Osaka Kyoiku University. Measurements of bias and dark counts, the read-out-noise, and of the linearlity show excellent performances of the camera. We also measured sky counts over the observatory, apparent stellar radius, and the statistical photometric precision of the observing system. The sky brightness is seriouly affected by the city light. The FWHM of the stellar image is, on the average, around 4 arc sec. Photometric precision of +/— 0.02 mag is achieved by the present system in measurements of 14-th magnitude stars.