CHARACTERIZING STELLAR FLARES IN THE ARIEL TARGETS: ACTIVITY ANALYSIS AND TRANSIT PROBABILITIES

The objective of this work is to investigate stellar flaring activity in confirmed exoplanet host stars of the Ariel Mission Candidate Sample (MCS), with the aim of assessing the impact of stellar flares on transit spectroscopy observations. From the Ariel sample, we select 290 nearby systems (d < 200 pc) with available TESS light curves, representative of the current Ariel target population. We analyze the light curves using an iterative Gaussian Process detrending and flare characterization pipeline, including injection--recovery tests to quantify detection completeness and biases. We identify 15,857 flares across 1,638 TESS sectors and model the cumulative flare energy distributions using two-segment power laws. The resulting flare statistics are used to estimate the probability of flare occurrence during planetary transit observations. We introduce the normalized flare activity index GF.01 to compare stellar activity levels across different bolometric luminosities, finding that approximately 3% of the sample exhibits enhanced flare activity (GF.01>1). The flare activity decreases with increasing stellar bolometric luminosity, indicating a higher relative flare output for lower-luminosity stars. Among the most active Ariel targets, AU Mic and HD 28109 show a high likelihood of flare contamination during transit observations. In particular, four out of five observed AU Mic b transits are affected by flares, consistent with the statistical expectations derived from the flare frequency distributions. By comparing predicted flare contamination probabilities with observed transit events, we validate the reliability of the framework and demonstrate that stellar flares can significantly affect Ariel transit observations. These results provide quantitative guidance for target selection, observation scheduling, and the development of mitigation strategies for flare-contaminated atmospheric spectra.