The Hot Neptune WASP-166 b with ESPRESSO – I. Refining the planetary architecture and stellar variability

In this paper, we present high-resolution spectroscopic transit observations from ESPRESSO of the super-Neptune WASP-166~b. addition to data, analyse photometric data {\sl TESS} six WASP-166~b transits along with simultaneous NGTS runs. These were used fit for planetary parameters as well assessing level stellar activity (e.g. spot crossings, flares) during observations. We utilise Reloaded Rossiter McLaughlin (RRM) technique spatially resolve surface, characterising centre-to-limb convection-induced variations, and refine star-planet obliquity. find has a projected obliquity $\lambda = -15.52^{+2.85}_{-2.76}$$^{\circ}$ $v\sin(i) 4.97 \pm 0.09$~kms$^{-1}$ which is consistent literature. able characterise convective variations result granulation on surface star order few kms$^{-1}$ first time. modelled using linear, quadratic cubic model being preferred. addition, by modelling differential rotation simultaneously retrieve potential anti-solar rotational shear ($\alpha \sim$ -0.5) inclination ($i_*$ either 42.03$^{+9.13}_{-9.60}$$^{\circ}$ or 133.64$^{+8.42}_{-7.98}$$^{\circ}$ if pointing towards away us). Finally, investigate how shape cross-correlation functions change function limb angle compare our results magnetohydrodynamic simulations.