Presentation #601.23 in the session Planet Detection - Radial Velocities.
Stellar spots play a crucial role in our understanding of stellar activity and its impact on exoplanet observations. In this talk, we present a detailed study of the active star WASP-85A and its transiting hot Jupiter, WASP-85Ab, using high-resolution spectroscopic data obtained with the ESPRESSO and HARPS-N spectrographs. Our spectroscopic observations are supported by simultaneous photometry using CHEOPS, NGTS and SPECULOOS. WASP-85A is known to exhibit prominent spots, making it an ideal candidate for a comprehensive investigation of spot-induced effects during planetary transits. Our analysis employs an enhanced version of the reloaded Rossiter-McLaughlin (RRM) method, tailored to account for the dynamic nature of stellar spots. By redefining the RRM method to incorporate spot-induced variations in the stellar radial velocity and spectral line profiles, we aim to provide a more accurate and detailed characterisation of the stellar surface features. The ESPRESSO spectrograph, with its high precision and resolution, allows us to discern subtle changes in the stellar spectrum during the transit, enabling a robust determination of the spot properties. We present the results of our analysis including the spectroscopic signature of individual spots on the stellar surface, their influence on the RM effect and planet atmosphere, and the implications for our understanding of stellar activity in exoplanet studies. Our study contributes valuable insights into the effect of stellar activity on exoplanet observations, emphasising the importance of a refined method for accurately characterising the obliquity and planetary atmospheres in the presence of active stellar surfaces. The synergistic combination of ESPRESSO’s observational capabilities with simultaneous ground and space-based photometry enhances our ability to unravel the intricate details of both stellar and planetary phenomena, advancing our understanding of exoplanetary systems in complex stellar environments.