Characterizing Stellar Flares in the ARIEL Targets: Activity Analysis and Transit Probabilities

The objective of this work is to investigate stellar flaring activity in the confirmed exoplanet host stars of the Ariel Mission Candidate Sample (MCS, July 2024 release), with the aim of assessing flare probabilities during transit spectroscopy. From the 657 stars included in the catalogue, we select a subsample of 290 nearby systems (d < 200 pc) with available TESS light curves, representative of the current Ariel target distribution. Light curves are analysed using an iterative Gaussian Process detrending and flare characterization technique described in Galletta et al. (2025), providing flare amplitudes, durations, and energies. For this population, we compute the cumulative flare energy distribution and derive power-law slopes, finding a mean value of −1.87 with a standard deviation of 1.55. Using these flare statistics, we estimate the probability of detecting a flare above a given energy threshold during a planetary transit. We find that for the most active stars in the Ariel sample , AU Mic, HD 28109, and WASP-14, the probability of a flare overlapping a transit can approach ~50%, potentially affecting atmospheric retrievals, noise budgets, and visit planning. Our results highlight the importance of incorporating flare statistics into Ariel mission strategy, both for optimizing scheduling and for developing dedicated correction methods for flare-contaminated spectra.