Hα Emission Variability in Active M Dwarfs

We use similar to 12, 000 spectra of similar to 3500 magnetically active M0-M9 dwarfs from the Sloan Digital Sky Survey taken at 10-15 minute intervals, together with similar to 300 spectra of similar to 60 M0-M8 stars obtained hourly with the Hydra multiobject spectrometer, to probe H alpha variability on timescales of minutes to weeks. With multiple observations for every star examined, we are able to characterize fluctuations in H alpha emission as a function of activity strength and spectral type. Stars with greater magnetic activity (as quantified by L-H alpha/L-bol) are found to be less variable at all spectral types. We attribute this result to the stronger level of persistent emission in the high-activity stars, requiring a larger heating event in order to produce measurable variability. We also construct H alpha structure functions to constrain the timescale of variability. The more active objects with lower variability exhibit a characteristic timescale longer than 1 hr, likely due to larger, longer lasting heating events, while the less active objects with higher variability have a characteristic timescale shorter than 15 minutes.