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arXiv 2203.01344astro-ph.SR
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活动中晚期M矮星H $α$的变化时标

Variability Timescales of H$α$ on Active Mid-to-Late M dwarfs

Amber A. Medina, David Charbonneau, Jennifer G. Winters, Jonathan Irwin, Jessica Mink

备注：
Accepted for publication in The Astrophysical Journal
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摘要：

本文研究了13颗质量在0.1- 0.3太阳质量之间、完全对流的活跃中晚期M星的色球活动指示器H $α$的变化时标。我们的目标是确定主要的变异时间尺度，并通过推理，一个可能的机制负责的变化。我们收集了10个或更多的高分辨率光谱，每10颗恒星使用TRES摄谱仪在选定的时间，以跨越所有阶段的恒星旋转，确定从测光数据从MEarth天文台。所有恒星的H $α$发射都不同。对于其中的9颗恒星，我们发现H $α$和旋转相位之间没有相关性，这表明来自固定磁性结构（如恒星黑子和斑）的恒定发射不太可能是H $α$发射变化的主要来源。与此相反，一颗恒星，G 7-34，显示了H $α$和恒星旋转相位之间的明确关系。有趣的是，我们发现这颗恒星是剑鱼座AB移动群的成员，因此年龄为1.49亿年。对另外三颗恒星的高节奏光谱观测表明，它们在20- 45分钟的时间尺度上是可变的，我们认为这可能是由于耀斑行为。对于一颗恒星GJ 1111，同步TESS测光和光谱监测显示，随着光度亮度的增加，H $α$的发射也增加。我们的结论是，低能量耀斑能够产生的H $α$的变化，我们观察到的时间尺度上，因此可能是H $α$变化的主要来源，对活跃的完全对流M矮星。

英文摘要：

We present a study of the variation timescales of the chromospheric activity indicator H$α$ on a sample of 13 fully-convective, active mid-to-late M stars with masses between 0.1--0.3 solar masses. Our goal was to determine the dominant variability timescale and, by inference, a possible mechanism responsible for the variation. We gathered 10 or more high-resolution spectra each of 10 stars using the TRES spectrograph at times chosen to span all phases of stellar rotation, as determined from photometric data from the MEarth Observatories. All stars varied in their H$α$ emission. For 9 of these stars, we found no correlation between H$α$ and rotational phase, indicating that constant emission from fixed magnetic structures, such as starspots and plage, are unlikely to be the dominant source of H$α$ emission variability. In contrast, one star, G 7-34, shows a clear relationship between H$α$ and stellar rotational phase. Intriguingly, we found that this star is a member of the AB Doradus moving group and hence has the young age of 149 Myr. High-cadence spectroscopic observations of three additional stars revealed that they are variable on timescales ranging from 20--45 minutes, which we posit may be due to flaring behavior. For one star, GJ 1111, simultaneous TESS photometry and spectroscopic monitoring show an increase in H$α$ emission with increased photometric brightness. We conclude that low-energy flares are able to produce variation in H$α$ on the timescales we observe and thus may be the dominant source of H$α$ variability on active fully-convective M dwarfs.

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