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

TL;DR

This study analyzes the evolution of stellar flare activity in young GKM stars under 300 million years over five years of TESS data, revealing saturation in flare frequency distribution and potential links to stellar activity cycles.

Contribution

It provides the first large-scale analysis of flare activity in young stars using TESS data, identifying saturation points and variability patterns in flare rates across different ages and spectral types.

Findings

Flare frequency distribution slope saturates at -0.5 for all spectral types.

Flare rates are saturated below Rossby number 0.14 for stars aged 50-250 Myr.

Evidence of annual flare rate variability possibly linked to activity cycles.

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 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 3,157 stars and robustly measure the rotation periods of 1,847 stars. We measure and find the flare frequency distribution (FFD) slope, $\alpha$, saturates for all spectral types at $\alpha \sim -0.5$ and is constant over 300 Myr. Additionally, we find that flare rates for stars $t_\textrm{age} = 50 - 250$ 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 cross match our entire sample with GALEX 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.