Seimei望远镜和TESS观测到的小犬YZ上的一次超耀斑：H $α$发射与白光发射的红色不对称性
A Superflare on YZ Canis Minoris Observed by Seimei Telescope and TESS: Red Asymmetry of H$α$ Emission Associated with White-Light Emission
摘要：
已知活跃的M型恒星经常在表面产生超级耀斑。来自恒星（超级）耀斑的辐射对系外行星的可居住性很重要，但其机制还不清楚。本文报道了用3.8米星明望远镜和$Transiting\, Exoplanet\, Survey\, Satellite$同时观测活动M矮星YZ CMi上的恒星超耀斑的光谱和光度。耀斑辐射热能量为$1.3^{+1.6}_{-0.6} \times 10^{34} \,\rm{erg}$，H $α$能量为$3.0^{+0.1}_{-0.1} \times 10^{32} \,\rm{erg}$。H $α$发射谱线轮廓在整个耀斑期间呈现红色不对称，持续时间为$4.6-5.1 \,\rm{hrs}$。红色不对称的速度为$\sim 200-500 \,\rm{km\,s^{-1}}$，H $α$的线宽增宽至$34 \pm 14$ $Å$。H $α$谱线的红移速度和谱线宽度的衰减比等效谱线宽度的衰减快，它们的时间演化与白光发射的时间演化相关。这表明白光、H $α$红色不对称性和H $α$谱线增宽起源于几乎相同的位点，即，由非热电子加热的致密色球凝聚区。另一方面，在耀斑爆发后1小时，红移的过剩分量与中心分量的通量比增强。这可能是由于在耀斑后期，红色不对称性的主要来源转变为耀斑后环的缘故。
英文摘要：
Active M-type stars are known to often produce superflares on the surface. Radiation from stellar (super-)flares is important for the exoplanet habitability, but the mechanisms are not well understood. In this paper, we report simultaneous optical spectroscopic and photometric observations of a stellar superflare on an active M dwarf YZ CMi with the 3.8-m Seimei telescope and the $Transiting\, Exoplanet\, Survey\, Satellite$. The flare bolometric energy was $1.3^{+1.6}_{-0.6} \times 10^{34} \,\rm{erg}$ and H$α$ energy was $3.0^{+0.1}_{-0.1} \times 10^{32} \,\rm{erg}$. The H$α$ emission line profile showed red asymmetry throughout the flare with a duration of $4.6-5.1 \,\rm{hrs}$. The velocity of the red asymmetry was $\sim 200-500 \,\rm{km\,s^{-1}}$ and line width of H$α$ was broadened up to $34 \pm 14$ $Å$. The redshifted velocity and line width of H$α$ line decayed more rapidly than the equivalent width, and their time evolutions are correlated with that of the white-light emission. This indicates a possibility that the white light, H$α$ red asymmetry, and H$α$ line broadening originate from nearly the same site, i.e., the dense chromospheric condensation region heated by non-thermal electrons. On the other hand, the flux ratio of the redshifted excess components to the central components is enhanced one hour after the flare onset. This may be due to the change of the main source of the red asymmetry to the post-flare loops in the later phase of the flare.
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