TOI-178 light curves

We performed a global analysis of all the available photometry from CHEOPS, TESS and NGTS, and radial velocity from ESPRESSO, using a photo-dynamical modelling of the light curve. We also tried different sets of priors on the masses and eccentricity, as well as different stellar activity models, to study their effects on the masses estimated by transit-timing variations (TTVs) and radial velocities (RVs). We demonstrate how stellar activity prevents a robust mass estimation for the three outer planets using radial velocity data alone.We also show that our joint photo-dynamical and radial velocity analysis has resulted in a robust mass determination for planets c to g, with precision of ~12% for the mass of planet c, and better than 10% for planets $d$ to g.

The new precisions on the radii range from 2 to 3%. The understanding of this synergy between photometric and radial velocity measurements will be valuable for the PLATO mission. We also show that TOI-178 is indeed currently locked in the resonant configuration, librating around an equilibrium of the chain.