[论文解读] Simultaneous photometric and CARMENES spectroscopic monitoring of fast-rotating M dwarf GJ 3270. Discovery of a post-flare corotating feature

E. N. Johnson, S. Czesla+34 more|arXiv (Cornell University)|Apr 14, 2021

Stellar, planetary, and galactic studies参考文献 82被引用 12

一句话总结

本研究对快速旋转的M型矮星GJ 3270开展了同步的高时间分辨率光变与CARMENES光谱观测，揭示了一次总能量约为3.6 × 10³² erg的强烈恒星耀斑，以及一次持续存在的耀斑后同步旋转特征，表现为色球层谱线的蓝移不对称性。这是首次在太阳以外的恒星上探测到此类特征，表明可能存在类似太阳的耀斑后拱形结构或失败的日冕物质抛射。

ABSTRACT

Context: Active M dwarfs frequently exhibit large flares, which can pose an existential threat to the habitability of any planet in orbit in addition to making said planets more difficult to detect. M dwarfs do not lose angular momentum as easily as earlier-type stars, which maintain the high levels of stellar activity for far longer. Studying young, fast-rotating M dwarfs is key to understanding their near stellar environment and the evolution of activity Aims: We study stellar activity on the fast-rotating M dwarf GJ 3270. Methods: We analyzed dedicated high cadence, simultaneous, photometric and high-resolution spectroscopic observations obtained with CARMENES of GJ 3270 over 7.7 h, covering a total of eight flares of which two are strong enough to facilitate a detailed analysis. We consult the TESS data, obtained in the month prior to our own observations, to study rotational modulation and to compare the TESS flares to those observed in our campaign. Results: The TESS data exhibit rotational modulation with a period of 0.37 d. The strongest flare covered by our observing campaign released a total energy of about 3.6e32 erg, putting it close to the superflare regime. This flare is visible in the B,V, r, i, and z photometric bands, which allows us to determine a peak temperature of about 10,000 K. The flare also leaves clear marks in the spectral time series. In particular, we observe an evolving, mainly blue asymmetry in chromospheric lines, which we attribute to a post-flare, corotating feature. To our knowledge this is the first time such a feature has been seen on a star other than our Sun. Conclusions: Our photometric and spectroscopic time series covers the eruption of a strong flare followed up by a corotating feature analogous to a post-flare arcadal loop on the Sun with a possible failed ejection of material.

研究动机与目标

• 研究快速旋转M型矮星GJ 3270的恒星活动，特别是耀斑及其后续影响。
• 理解高恒星活动对行星宜居性与探测的影响。
• 利用同步多波段观测研究晚型星中耀斑后现象的本质。
• 在活跃的M型矮星中搜寻日冕物质抛射或失败抛射的特征。

提出的方法

• 在7.7小时内，利用CARMENES对GJ 3270进行了同步的高时间分辨率光变与高分辨率光谱监测。
• 分析了观测活动开始前一个月的TESS数据，以研究自转调制效应与耀斑能量分布。
• 利用B、V、r、i和z波段的光变曲线，确定耀斑峰值温度与总能量。
• 对色球层谱线（Hα、Na D、He i D3、Ca ii IRT）进行详细的光谱时间序列分析，以探测谱线不对称性与多普勒位移。
• 对谱线不对称性的运动学进行建模，以推断同步旋转表面特征及其起源。
• 将观测到的耀斑演化过程与太阳类比，以解释耀斑后特征的性质。

实验结果

研究问题

• RQ1 在GJ 3270上观测到的最强耀斑的能量输出与热演化特性如何？
• RQ2 M型矮星耀斑后的色球层谱线不对称性是否可与太阳耀斑后拱形结构类似的同步旋转活动区结构相关联？
• RQ3 为何在耀斑1期间，钠D线与He i D3线的响应强于Hα线？这对其耀斑位置有何启示？
• RQ4 主耀斑之后是否存在日冕雨或回流等离子体运动的证据？
• RQ5 在耀斑衰减阶段，持续存在的蓝移谱线成分是否可推断出失败的日冕物质抛射？

主要发现

• 观测到的最强耀斑总能量约为3.6 × 10³² erg，处于超级耀斑的范畴。
• 根据B、V、r、i和z波段的波段光度测量，该耀斑的峰值温度约为10,000 K。
• 在耀斑后约90分钟内，观测到Hα线存在持续的蓝移不对称性，其中窄成分蓝移达25.9 km s−1。
• 该蓝移成分与Na D线和He i D3线的类似位移相关，表明存在整体的等离子体上升运动。
• 该特征的多普勒位移与衰减速率与位于距盘心约65°、纬度约40°的同步旋转表面结构一致。
• 在耀斑后出现一段色球层谱线红移不对称性增强的时期——无同时耀斑活动——表明可能存在强烈的日冕雨或回流等离子体，可能源自一次失败的CME。