The characterisation of exoplanetary systems - From stellar to planetary parameters

mardi 5 novembre 2019, par Roxanne Ligi (Osservatorio Astronomico di Brera, Italy)

Lundi 9 décembre 2019 à 14h30 , Lieu : Salle de conférence du bâtiment 17

The harvest of transiting exoplanets discoveries has led to the quest of their characterisation. However, the radius, mass and density of exoplanets totally rely on the host star parameters. But interferometry allows to measure the stellar radius and the transit light curves give the stellar density. This directly yields the stellar mass, a parameter that cannot be directly measured otherwise.

We applied this method to the systems of 55 Cnc and HD219134 which host one and two transiting exoplanets, respectively. Thanks to the newly measured stellar and exoplanets parameters, we derived the exoplanets internal compositions using an inference scheme. We show that, contrary to what previous studies show, the transiting exoplanet 55 Cnc e may only have a thin atmosphere and its interior structure might not be dominated by carbon. Our new radii for HD219134 b and c remove them from the "Fulton gap" and thus suggest a rocky nature. The lower density of the inner more massive planet could then be explained by a molten interior possibly induced by tidal heating caused by a high eccentricity during its formation.

Transiting exoplanets around bright stars constitute benchmark systems to investigate exoplanet properties and calibrate stellar models. With the on-sky TESS satellite and the forthcoming mission PLATO, we will be able to extensively apply this method, and thus revisit exoplanets populations and deepen our knowledge of stellar evolution.