Challenging Na detections in the atmospheres of giant planets with 3D non-LTE stellar spectra

Transmission spectroscopy from high-resolution ground-based spectrographs is one of the most powerful techniques for characterizing the atmospheres of giant exoplanets. Previous studies have highlighted the importance of correcting the transmission spectra for the center-to-limb variation (CLV) and the Rossiter-McLaughlin (RM) effect arising as the planet transits the stellar disk. If not properly corrected, these effects can indeed resemble or cancel out planetary absorption in certain cases, thus affecting the determination of elemental abundances in the planetary atmospheres.

However, commonly used 1D plane-parallel LTE atmosphere models fail to reproduce spatially resolved observations of the solar disk. 3D radiation hydrodynamic models and non-local thermodynamic equilibrium (non-LTE) line formation are required for an accurate modeling of the CLV effect.

Sodium is by far the most detected species in transmission spectra, through the analysis of the Na I D lines, which are affected by strong 3D non-LTE effects.

In this talk, I will present new results regarding the analysis of these lines in ESPRESSO data of several benchmark gas giants, by modeling their CLV and RM effect using 3D non-LTE radiative transfer. These kinds of studies will be fundamental in preparation for the ELT in order to be able to fully exploit its capabilities in the near future.