M Dwarf Flares from Time-Resolved SDSS Spectra

TL;DR

This study identifies 63 flares on M dwarfs using SDSS spectra, revealing that flare frequency increases with later spectral types and is higher among younger, near-Galactic plane stars, indicating a link to stellar age.

Contribution

Introduces a novel emission line measurement method to detect flares in SDSS spectra and characterizes flare occurrence across M dwarf spectral types and spatial distributions.

Findings

Flare duty cycle increases from 0.02% to 3% from early to late M dwarfs.

Flares are more common in stars near the Galactic plane.

Flare stars tend to be younger than the average active population.

Abstract

We have identified 63 flares on M dwarfs from the individual component spectra in the Sloan Digital Sky Survey using a novel measurement of emission line strength called the Flare Line Index. Each of the ~38,000 M dwarfs in the SDSS low mass star spectroscopic sample of West et al. was observed several times (usually 3-5) in exposures that were typically 9-25 minutes in duration. Our criteria allowed us to identify flares that exhibit very strong H-alpha and H-beta emission line strength and/or significant variability in those lines throughout the course of the exposures. The flares we identified have characteristics consistent with flares observed by classical spectroscopic monitoring. The flare duty cycle for the objects in our sample is found to increase from 0.02% for early M dwarfs to 3% for late M dwarfs. We find that the flare duty cycle is larger in the population near the Galactic plane and that the flare stars are more spatially restricted than the magnetically active but non-flaring stars. This suggests that flare frequency may be related to stellar age (younger stars are more likely to flare) and that the flare stars are younger than the mean active population.