MODELING OF STELLAR ACTIVITY OF STARS HOSTING PLANETS

Stellar activity is one of the main sources of noise in exoplanet observations, especially for planets orbiting around young stars, because they are characterized by a high level of variability that affects both the spectroscopic and photometric observations. To study planet formation in young planetary systems and achieve a level of precision high enough to study exoplanets atmospheres, we need to model the stellar activity, both through spectroscopy and photometry, to correct its effects in the observations. As a prototype of a very active star, we observed and modeled the very young star V1298 Tau, hosting a multi-planetary system, through multiband photometry characterizing its active regions after validating the method on solar data. We also developed a technique to simulate stellar activity effects on transiting planetary spectra. The simulations were used to verify our atmospheric retrieval capability and establish the level of complexity necessary for achieving the corrections needed to correctly interpret low-resolution spectroscopic data. Finally, we analyzed LHS 1140b HST low-resolution transit spectra to test the level of activity of the star and its effect on the retrieval of the atmospheric composition of the planet. In this specific case, we found that the spectrum distortions are not due to star activity but to the non-solar stellar composition of the target. This is a warning for future studies to test if in some cases signals attributed to activity are in fact due to a wrong estimation of stars’ composition, and to outline the need to characterize very well the host star.