An ESPRESSO view of HD 189733 system. Broadband transmission spectrum, differential rotation, and system architecture

The development of state-of-the-art spectrographs has ushered in a new era in the detection and characterization of exoplanetary systems. Our objective is to utilize the high-resolution and precision capabilities of the ESPRESSO instrument to detect and measure the broad-band transmission spectrum of HD 189733b's atmosphere. Additionally, we aim to employ an improved Rossiter-McLaughlin model to derive properties related to the velocity fields of the stellar surface and to constrain the orbital architecture. Our results demonstrate a high degree of precision in fitting the observed radial velocities during transit using the improved modeling of the Rossiter-McLaughlin effect. We tentatively detect the effect of differential rotation with a confidence level of 93.4 % when considering a rotation period within the photometric literature values, and 99.6% for a broader range of rotation periods. For the former, the amplitude of differential rotation ratio suggests an equatorial rotation period of 11.45± 0.09 days and a polar period of 14.9± 2. The addition of differential rotation breaks the latitudinal symmetry, enabling us to measure the true spin-orbit angle ψ≈ 13.6 ± 6.9 ^∘ and the stellar inclination axis angle i_⋆≈ 71.87 ^+6.91^∘_-5.55^∘. Moreover, we determine a sub-solar amplitude of the convective blueshift velocity V_CB ≈ -211 ^+69 _-61 ms^-1, which falls within the expected range for a K-dwarf host star and is compatible with both runs. Finally, we successfully retrieved the transmission spectrum of HD 189733b from the high-resolution ESPRESSO data. We observe a significant decrease in radius with increasing wavelength, consistent with the phenomenon of super-Rayleigh scattering.