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Title: Variability Timescales of Hα on Active Mid-to-late M dwarfs

We present a study of the variation timescales of the chromospheric activity indicator Hαon a sample of 13 fully convective, active mid-to-late M stars with masses between 0.1 and 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 Hαemission. For nine of these stars, we found no correlation between Hαand rotational phase, indicating that constant emission from fixed magnetic structures, such as star spots and plage, are unlikely to be the dominant source of Hαemission variability. In contrast, one star, G 7–34, shows a clear relationship between Hαand 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 to 45 minutes, which we posit may be due to flaring behavior. For one star, more » GJ 1111, simultaneous TESS photometry and spectroscopic monitoring show an increase in Hαemission with increased photometric brightness. We conclude that low-energy flares are able to produce variation in Hαon the timescales we observe and thus may be the dominant source of Hαvariability on active fully convective M dwarfs.

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Publication Date:
Journal Name:
The Astrophysical Journal
Page Range or eLocation-ID:
Article No. 185
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation
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