On the correlation between starspot activity and superflares on solar-type stars

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05400
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Astronomy
• Research Institution: National Astronomical Observatory of Japan (2018-2019); Kyoto University (2017)
• Principal Investigator: Maehara Hiroyuki 国立天文台, ハワイ観測所, 助教 (40456851)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 太陽型星 / 黒点 / フレア

Outline of Final Research Achievements

We studied the occurrence frequency and lifetime of large starspots which can produce "superflares" on solar-type stars by using photometric data by Kepler space telescope and ground-based long-term observations. We found that the size distribution of large starspots on solar-type stars as a function of the area of starspots shows the power-law distribution. Our results suggest that the size distribution of starspots on solar-type stars and that of sunspots lie on the same power-law line. We also analyzed the lifetime of starspots on solar-type stars from the rotational brightness modulations and found that larger starspots tend to have longer lifetime. The lifetime of large starspots on solar-type stars is consistent with that predicted from the lifetime-area relation for sunspots. Our findings imply that both sunspots and larger starspots on solar-type stars are caused by the same physical mechanisms.

Free Research Field

光赤外線天文学

Academic Significance and Societal Importance of the Research Achievements

本研究で得られた研究結果から、スーパーフレアを起こしうる巨大黒点の発生頻度や寿命を初めて明らかにすることができ、それらが従来の太陽観測から知られていた黒点の発生頻度と面積の関係や、寿命と面積の関係の延長線上にのることが明らかとなった。このことは、スーパーフレアを起こすような巨大黒点と太陽で見られる黒点は、同じメカニズムで生成・発展・消滅することを示唆する。さらに、太陽でもスーパーフレアを起こすような巨大黒点が発生しうることを示唆しており、本研究の結果は太陽でのスーパーフレアに伴う巨大磁気嵐等の地球上の文明社会への影響やそのリスク評価にとっても重要である。