Monday

As the Sun is our nearest star, detailed spatial and temporal observations have been collected for centuries offering vast opportunities to study its phenomena. As a result, these phenomena are relatively well understood with this knowledge being applied to other stars. Stellar physics can impact important exoplanet parameters such as radii, mass, and planet atmosphere determinations. Therefore, characterising a star in great detail is vital for understanding exoplanets. Furthermore, understanding stellar physics can be crucial when searching for low mass, long period planets (Earth-twins) due to signals being lost within stellar ‘noise’. In this talk, we will present our most recent results utilising the reloaded Rossiter-McLaughlin (RRM) technique on the 2016 Sun/Mercury transit with HARPS-N and SDO. When a planet transits a host star, a portion of the starlight is blocked from the line of sight and a distortion of the velocities is observed, known as the Rossiter-McLaughlin (RM) effect. In the RRM, we use transiting planets to probe and spatially resolve the star, investigating stellar properties such as differential rotation and centre-to-limb convective variations. By doing this we are able to measure the differential rotation and use it to decouple the projected equatorial velocity of the star, to measure the stellar inclination. We can combine this with the projected obliquity to determine the true 3D obliquity (i.e. the geometry of the star-planet system), which are of particular importance when considering
planet formation, migration, and evolution. Overall, the Sun/Mercury system is well known and can be used as a test (we already know the solar and planetary properties) allowing for further validation of the RRM method and will aid in exploring potential degeneracies.