Evolution of Flare Activity in GKM Stars Younger Than 300 Myr over Five Years of TESS Observations

Abstract

Stellar flares are short-duration (< hours) bursts of radiation associated with surface magnetic reconnection events. Stellar magnetic activity generally decreases as a function of both the age and Rossby number, R _0 , a measure of the relative importance of the convective and rotational dynamos. Young stars (<300 Myr) have typically been overlooked in population-level flare studies due to challenges with flare-detection methods. Here, we select a sample of stars that are members of 26 nearby moving groups, clusters, or associations with ages <300 Myr that have been observed by the Transiting Exoplanet Survey Satellite at 2 minute cadence. We identified 26,355 flares originating from 3160 stars and robustly measured the rotation periods of 1847 stars. We measure and find the flare frequency distribution slope, α , saturates for all spectral types at α ∼ −0.5 and is constant over 300 Myr. Additionally, we find that flare rates for stars t _age = 50–250 Myr are saturated below R _0 < 0.14, which is consistent with other indicators of magnetic activity. We find evidence of annual flare rate variability in eleven stars, potentially correlated with long-term stellar activity cycles. Additionally, we crossmatch our entire sample with the Galaxy Evolution Explorer and find no correlation between flare rate and far- and near-ultraviolet flux. Finally, we find the flare rates of planet-hosting stars are relatively lower than comparable, larger samples of stars, which may have ramifications for the atmospheric evolution of short-period exoplanets.

Keywords

• Pre-main sequence stars
• Optical flares
• Stellar rotation
• Stellar activity
• Time series analysis