Enhancing the detection of low-energy M dwarf flares: Wavelet-based denoising of CHEOPS data

Abstract

Stellar flares are powerful bursts of electromagnetic radiation triggered by magnetic reconnection in the chromosphere of stars, occurring frequently and intensely on active M dwarfs. While missions like TESS and Kepler have studied regular and super-flares, their detection of flares with energies below $10^{30}$ erg remains incomplete. Extending flare studies to include these low-energy events could enhance flare formation models and provide insight into their impacts on exoplanetary atmospheres. This study investigates CHEOPS's capacity to detect low-energy flares in M dwarf light curves. Using its high photometric precision and observing cadence, along with a tailored wavelet-based denoising algorithm, we aim to improve detection completeness and refine flare statistics for low-energy events. We conducted a flare injection and recovery to optimise denoising parameters, applied it to CHEOPS light curves to maximise detection rates, and used a flare breakdown algorithm to analyse complex structures. We recovered 291 flares with energies ranging from $3.7\times 10^{26}$ to $8.9\times 10^{30}$ erg across 62 M dwarfs, with $\sim$42% exhibiting complex, multi-peaked structures. The denoising improved flare recovery by $\sim$35%, although it marginally extended the lower boundary of detectable energies. For the full sample, the power-law index $\alpha$ was $1.99\pm 0.10$, but a log-normal distribution fitted better, suggesting multiple possible flare formation scenarios. While CHEOPS's observing mode is not ideal for large-scale surveys, it captures weaker flares than TESS or Kepler, expanding the observed energy range. Wavelet-based denoising enhances low-energy event recovery, enabling exploration of the micro-flaring regime. Expanding low-energy flare observations could refine flare generation models and improve the understanding of their role in star-planet interactions.

29 pages, 20 figures, 4 tables, Accepted for publication in A&A

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• The largest ground-based catalogue of M-dwarf flares