Young solar-type stars are known to show frequent "superflares", which may severely influence the habitable worlds on young planets via intense radiations and coronal mass ejections. Here we report an optical spectroscopic and photometric observation of a long-duration superflare on the young solar-type star EK Draconis (50-120 Myr age) with the Seimei telescope and $Transiting$ $Exoplanet$ $Survey$ $Satellite$ ($TESS$). The flare energy 2.6$\times$10$^{34}$ erg and white-light flare duration 2.2 hr are much larger than those of the largest solar flares, and this is the largest superflare on a solar-type star ever detected by optical spectroscopy. The H$α$ emission profile shows no significant line asymmetry, meaning no signature of a filament eruption, unlike the only previous detection of a superflare on this star (Namekata et al. 2021, $Nat.Astron$). Also, it did not show significant line broadening, indicating that the non-thermal heating at the flare footpoints are not essential or that the footpoints are behind the limb. The time evolution and duration of the H$α$ flare are surprisingly almost the same as those of the white-light flare, which is different from general M-dwarf (super-)flares and solar flares. This unexpected time evolution may suggest that different radiation mechanisms than general solar flares are predominant, as follows: (1) radiation from (off-limb) flare loops, and (2) re-radiation via radiative backwarming, in both of which the cooling timescales of flare loops could determine the timescales of H$α$ and white light.
Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. II. Understanding Prominence Eruption through Data-Driven Modeling and Observed Magnetic Environment
AstroSat observations of long-duration X-ray superflares on active M-dwarf binary EQ Peg
We present a comprehensive study of three large long-duration flares detected on an active M-dwarf binary EQ Peg using the Soft X-Ray Telescope of the AstroSat observatory. The peak X-ray luminosities of the flares in the 0.3 - 7 keV band are found to be within ~5 - 10 x 10^{30} erg s^{-1}. The e-folding rise- and decay-times of the flares are derived to be in the range of 3.4 - 11 and 1.6 - 24 ks, respectively. Spectral analysis indicates the presence of three temperature corona with the first two plasma temperatures remain constant during all the flares and the post-flare observation at ~3 a…
Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. III. Comparison between Starspot Mapping, Zeeman Doppler Imaging, and Multiwavelength Variability
Hitotsubashi University（一桥大学）；The University of Tokyo（东京大学）；The Hakubi Center for Advanced Research, Kyoto University（京都大学博雅研究高级中心）；Department of Physics, Kyoto University（京都大学物理学系）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Department of Physics, The Catholic University of America（美利坚天主教大学物理学系）；Division of Science, National Astronomical Observatory of Japan, NINS（日本国立天文台科学部）；Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES（图卢兹大学、法国国家科学研究中心、法国国家空间研究中心天体物理与行星学研究所在）；Department of Physics, American University（美国大学物理学系）
Time-Resolved Connection between Starspots and Flares in Nearby Young Solar-type Stars Observed by TESS
Kyoto University（京都大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；The Catholic University of America（美利坚天主教大学）；The Hakubi Center for Advanced Research, Kyoto University（京都大学Hakubi高级研究中心）
Optical Flares Detected on a Contact Binary: The First Photometric and Spectroscopic Analysis of a Long-period Low Mass Ratio Contact Binary HAT 307-0007476
Summary of the First Year of the Space Weather Around Young Suns Program: 900 Hours of Low-frequency Radio and Optical Data Dedicated to Young, Solar-type Stars
Cahill Center for Astronomy and Astrophysics, California Institute of Technology（加州理工学院卡希尔天文与天体物理中心）；Owens Valley Radio Observatory, California Institute of Technology（加州理工学院欧文斯谷射电天文台）；ASTRON, Netherlands Institute for Radio Astronomy（荷兰射电天文研究所 ASTRON）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Caltech Optical Observatories, California Institute of Technology（加州理工学院光学天文台）；School of Earth and Space Exploration, Arizona State University（亚利桑那州立大学地球与空间探索学院）
Are Starspots and Plages Co-Located on Active G and K Stars?
通过研究三颗主序星在几个自转周期内的色球和光球活动，探讨了它们的星斑和谱斑之间的联系。我们提出了同步测光和高分辨率（$R\sim 31,500$）光谱的KIC 9652680，一个年轻的，超耀斑生产的G1恒星的旋转周期为1.4天。它的开普勒光变曲线显示旋转调制与明亮的半球相一致，然后是相对较暗的半球，产生半振幅为4%的光度变化。我们发现，KIC 9652680是最黑暗的时候，它的$S$ -指数的钙II H & K的发射是在其最大值。我们解释了通量和$S$之间的反相关性，表明光球层中的暗恒星黑子与色球层中的亮斑位于同一位置，就像它们在太阳上一样。移动到较低的质量和较慢的旋转，我们目前的K2观测与EPIC 211928486（K5 V）和EPIC 211966629（K4 V），两个活跃的恒星在6.5亿岁的疏散星团Praesepe的同时光谱。K2测光显示，这两颗恒星的自转周期都是11.7天;虽然它们的流量分别变化了1%和2%，但它们的Ca II H & K $S$指数似乎保持相对恒定，作为旋转相位的函数。这表明扩展的色球网络并不像KIC 9652680那样集中在以驱动旋转调制的恒星黑子为中心的发射区域。我们还注意到EPIC 211928486的Ca II发射在一个旋转周期内突然下降和恢复，这表明谱斑的演化时间尺度可能是旋转周期的量级。
X-ray Activity of the RS CVn-type Star σ Gem with the First-Year Observations of Einstein Probe
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文学院）；INAF - Osservatorio Astronomico di Palermo（意大利国家天体物理研究所巴勒莫天文台）；Department of Physics, Imperial College London（伦敦帝国理工学院物理系）
