Characterizing a set of small planet candidates bordering the radius valley with TESS and CHEOPS observations

The NASA Transiting Exoplanet Survey Satellite (TESS) mission has searched the entire sky for transiting exoplanets around the nearest, brightest stars. The planets it has and will discover have the potential to gradually populate the small planet mass-radius parameter space with tightly constrained bulk densities, which are vital pieces to improving our understanding of the radius valley at 1.5-2.0 Earth radii and how it is shaped by atmospheric mass-loss processes. We present precise radius measurements and orbital parameters for a set of TESS Objects of Interest (TOIs) with estimated radii from 1.3 to 4.3 Earth radii. These planets have also been observed by the ESA CHaracterising ExOPlanets Satellite (CHEOPS) mission, which has a larger light-collecting area compared to TESS, allowing for exquisite characterization. Transits obtained by CHEOPS not only allow for the radii of these targets to be more tightly constrained, but also other orbital parameters such as eccentricity, which allow us a closer glimpse into the architectures of these systems. We compare CHEOPS and TESS parameters for these TOIs, specifically examining differences in transit depths and their uncertainties. We also explore possible reasons as to why observations from these telescopes may give different results for these parameters, and whether different fitting algorithms may — at least sometimes — be causing these differences.