Characterising the Young Resonant Planetary System TOI-1136 with a Joint Stellar Activity and Photodynamical Analysis

TOI-1136 is a young planetary system exhibiting signs of orbital resonance, making it a valuable target for studying planetary dynamics in early evolutionary stages. In this thesis, we characterise the system’s physical properties and orbital architecture, carrying out for the first time a joint stellar activity and photodynamical analysis of TOI-1136. Photometric light curves from TESS and radial velocity measurements from HARPS-N, HIRES, and APF were used to model transits, transit timing variations (TTVs), and stellar activity signals with the PyORBIT software. Planetary orbits were computed using N-body simulations, which were then employed to model the transit light curves, while stellar activity was described with Gaussian process regression. This combined modelling framework improves the accuracy of radial velocity fits and accounts for gravitational interactions between the planets, enabling tighter constraints on their orbital parameters. The results were compared against a set of alternative analyses with different inputs, including non-dynamical photometric fits and exclusively spectroscopic analyses. We found that, although the photodynamical approach can yield accurate orbital parameter estimates—as demonstrated in a benchmark analysis of the two-planet system TOI-1130—it fell short of the expected accuracy for the more complex TOI-1136 system. Even so, the joint photodynamical and stellar activity analysis provided reasonably reliable estimates for the planets’ orbital periods, radii, and inferior conjunction times, though mass determinations remained inconsistent. Moreover, the combined spectroscopic and TTV analysis produced stellar parameters consistent with those from the photodynamical analysis. Overall, the results of this work contribute to a deeper understanding of the formation and dynamical evolution of young resonant planetary systems and help refine future applications of photodynamical techniques for exoplanet characterisation.