Searching for Stellar Activity Cycles using Flares: The Short and Long Timescale Activity Variations of TIC-272272592

TL;DR

This study analyzes four years of Kepler and TESS data for a rapidly rotating M dwarf star to investigate stellar activity cycles through flare frequency variations, introducing a new method for quantifying magnetic activity changes.

Contribution

It develops a novel approach to measure flare frequency distribution variations over time, aiding in understanding stellar magnetic activity cycles.

Findings

Detected short-term flare rate variation possibly due to sampling

Found evidence for both short and long timescale activity variations

Highlighted challenges in comparing data across different telescopes

Abstract

We examine 4 years of Kepler 30-min data, and 5 Sectors of TESS 2-min data for the dM3 star KIC-8507979/TIC-272272592. This rapidly rotating (P=1.2 day) star has previously been identified as flare active, with a possible long-term decline in its flare output. Such slow changes in surface magnetic activity are potential indicators of Solar-like activity cycles, which can yield important information about the structure of the stellar dynamo. We find that while TIC-272272592 shows evidence for both short and long timescale variations in its flare activity, it is unlikely physically motivated. Only a handful of stars have been subjected to such long baseline point-in-time flare studies, and we urge caution in comparing results between telescopes due to differences in bandpass, signal to noise, and cadence. In this work, we develop an approach to measure variations in the flare frequency distributions over time, which is quantified as a function of the observing baseline. For TIC-272272592, we find a $2.7\sigma$ detection of a Sector which has a flare deficit, therefore indicating the short term variation could be a result of sampling statistics. This quantifiable approach to describing flare rate variation is a powerful new method for measuring the months-to-years changes in surface magnetic activity, and provides important constraints on activity cycles and dynamo models for low mass stars.