Presentation #106.04 in the session Stars and Planets 1.
Characterising a star in great detail is a vital tool for understanding exoplanets. This is because stellar physics can impact important exoplanet parameters such as radii, mass, and planet atmosphere determinations. Additionally, 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, I will present my most recent results on WASP-166 b a transiting super-Neptune, within the Neptune desert, orbiting a bright (V = 9.36), F9 dwarf, utilising high-resolution spectroscopic transit observations from ESPRESSO. We utilise the Reloaded Rossiter McLaughlin (RRM) technique to spatially resolve the stellar surface, characterising the centre-to-limb convection-induced variations, and refine the star-planet obliquity. The net convective velocity shift caused by granules changes as a function of limb angle (i.e. from the centre to the limb of the star) due to line-of-sight changes. Since WASP-166 is an F-type main sequence star (Teff = 6050 K), we were able to characterise centre-to-limb convective variations (CLV) as a result of granulation on the surface of the star on the order of a few kms-1. It has been predicted that if neglected these velocity shifts can induce uncertainties in the projected obliquity and as a result skew our understanding of formation/evolution. For WASP-166 from our ESPRESSO observations, when CLV was not accounted for in our RM models there is a difference of 8.6o, which is in line with predictions. In addition to computing the RRM, we also take a closer inspection of the cross-correlation functions (CCFs) themselves and how their shape changes as a function of limb angle. We found that the FWHM and equivalent width show trends which increase towards the limb of the star by ~2 km s-1. Overall, this solidifies predictions and shows the effects CLV can have on the shape of the CCFs. Finally, we looked at the asymmetry in the CCF by fitting for the core and wing separately, finding the wing was more blue-shifted than the core. This is most likely related to the wings being formed deeper in the photosphere than the core, experiencing different shifts which are more prominent at the limb.