Correcting Stellar Flare Frequency Distributions Detected by TESS and Kepler

TL;DR

This study develops a unified method to correct for observational biases in stellar flare frequency distributions from Kepler and TESS data, revealing consistent flare behaviors across different stars after correction.

Contribution

It introduces a unified data processing and correction technique for flare detection in Kepler and TESS light curves, extending the low-energy limit of flare analysis and analyzing the flare frequency distribution dependence on stellar temperature.

Findings

Corrected flare frequency distributions are consistent between Kepler and TESS.

Extended the low-energy limit of flare analysis to 10^{31.5-33} erg.

Found the power-law index of flare distributions varies with stellar effective temperature.

Abstract

The habitability of planets is closely connected with the stellar activity, mainly the frequency of flares and the distribution of flare energy. Kepler and TESS find many flaring stars are detected via precise time-domain photometric data, and the frequency and energy distribution of stellar flares on different types of stars are studied statistically. However, the completeness and observational bias of detected flare events from different missions (e.g. Kepler and TESS) vary a lot. We use a unified data processing and detection method for flares events based on the light curve from Kepler and TESS. Then we perform injection and recovery tests in the original light curve of each star for each flare event to correct the completeness and energy of flares. Three samples of flaring stars are selected from Kepler and TESS, with rotating periods from 1 to $\sim$ 5 days. Adopting a hot-blackbody assumption, our results show that the cumulative flare frequency distributions (FFDs) of the same stars in Kepler and TESS bands tend to be consistent after correction, revealing a more natural flaring frequency and energy distribution. Our results also extend the low-energy limit in cumulative FFD fitting to $10^{31.5-33}$ erg on different types of stars. For solar-type stars, the average power-law index of cumulative FFD ($\alpha_{\rm cum}$) is $-0.84$, which indicates that low-energy flares contribute less to the total flare energy. With a piecewise correlation between $\alpha_{\rm cum}$ and $T_{\rm eff}$, $\alpha_{\rm cum}$ first rises with $T_{\rm eff}$ from M2 to K1 stars, then slightly decreases for stars hotter than K1.