High-resolution spectroscopy of WASP-31b with ESPRESSO

Over 5500 exoplanets have been discovered, predominantly through transits on short orbits. Notably, hot Jupiters and the absence of Neptune-sized planets (Neptune desert) have been identified, thanks to missions like Kepler. These types of planets can be very different in density, mainly due to the radius-inflation effect, whose origin is unclear. This, in particular, changes the atmospheric properties and chemical composition, which can be extracted through transmission spectroscopy at both low and high resolution. Furthermore, at high resolution, we can also observe the Rossiter-McLaughlin effect, providing us with the projected spin-orbit angle, an excellent probe into the dynamical history of the system. We will show the results of high-resolution transmission spectroscopy and the Rossiter-McLaughlin effect of WASP-31 b, a Jupiter-sized planet, using the ESPRESSO spectrograph.This planet has already been studied by a plethora of instruments. In particular, Sing+2016 found, using HST/STIS, an extremely strong signature of potassium. However, Gibson+2017 and later Gibson+2019, using VLT/FORS2 and VLT/UVES respectively, contradicted this signature. Furthermore, Flagg+2023 and later Flagg+2024 found CrH for the first time in an exoplanet's atmosphere. Brown+2017 analyzed the Rossiter-McLaughlin signature of this planet, which shows WASP-31b to be aligned (projected obliquity, ).In this analysis, we focused on the species sodium (Na), potassium (K), and iron (Fe). We also used the CrH template, although it is weaker in the wavelength range of ESPRESSO.