The physical environment when stellar hyper flares occur

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K05392
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Astronomy
• Research Institution: Chuo University
• Principal Investigator: Tsuboi Yohko 中央大学, 理工学部, 教授 (70349223)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: フレア / X線天文 / 可視光観測

Outline of Final Research Achievements

(1) We searched for super flares, which occur extremely infrequently, using the MAXI all-sky X-ray monitor, and made follow-up observations at various wavelengths. As a result, we obtained several correlations of physical quantities over many orders of magnitude, and statistically constrained the volume, shape, and loop length of the plasma loop almost for the first time. (2) We confirmed the existence of a proto-brown dwarf or a protostar with a very low mass and a age as young as about 1,000 yr, by multi-wavelength observations, and provided constraints on the age and mass at which the star begins to emit X-rays. (3) We made an optical system with high sensitivity to polarization, which provides information on the geometry and position of flare loops, using CFRP and thin Si crystals. Then we confirmed extremely high spectral resolution and polarization sensitivity.

Free Research Field

X線天文学

Academic Significance and Societal Importance of the Research Achievements

人類の文化的生活を脅かすような巨大なフレアが我々の太陽で起こるか否かは切実な問題である。本研究では、ハイパーフレアとも呼ぶべき、太陽フレアの最大規模に比べても６桁も大きいフレアのサーチを全天に対して行い、その発生機構についてさまざまな制限を与えた。ハイパーフレアにおけるフレアループの大きさを明らかにし、それが星自体の半径の１０倍以上にもなりえることや、その断面積が星表面の巨大黒点と同程度であること、などである。これは逆に言えば、太陽では巨大な黒点が出現して初めて巨大フレアが起こるであろうことを示唆する。またフレアの幾何を明らかにするX線偏光計の優れた性能を実測し、実現化を進めた。