The GAPS Programme at TNG : LXIX. The dayside of WASP-76 b revealed by GIANO-B, HARPS-N, and ESPRESSO: Evidence of 3D atmospheric effects

Context. The study of the atmosphere of ultra-hot Jupiters (UHJs) with equilibrium temperatures ≥2000 K provides valuable insights into atmospheric physics under such extreme conditions. Aims. We aim to characterise the dayside thermal spectrum of the UHJ WASP-76 b and investigate its properties. We analysed data gathered with three high-resolution spectrographs: specifically two nights with simultaneous observations of HARPS-N and GIANO-B, and four nights of publicly available ESPRESSO optical spectra. We observed the planet’s dayside, covering orbital phases between quadratures (0.25 < ϕ < 0.75). Methods. We performed a homogeneous analysis of the GIANO-B, HARPS-N, and ESPRESSO data and co-added the signal of thousands of planetary lines through cross-correlation with simulated spectra of the planetary atmosphere. Results. We report the detection of CO in the dayside atmosphere of WASP-76 b with a signal-to-noise ratio (S/N) of 10.4 in the GIANO-B spectra. In addition, we detect Fe I in both the HARPS-N and ESPRESSO datasets, with S/N values of 3.5 and 6.2, respectively. A signal from Fe I is also identified in one of the two GIANO-B observations, with an S/N of 4.0. Interestingly, a qualitatively similar pattern – with a weaker detection in one epoch compared to the other – is also observed in the two HARPS-N nights. The GIANO-B results are, therefore, consistent with those obtained with HARPS-N. Finally, we compared our strongest detections of CO (GIANO-B) and Fe I (ESPRESSO), with predictions from global circulation models (GCM). Both cross-correlation and likelihood analyses favour the GCM that includes atmospheric dynamics over a static (no-dynamics) model when applied to the ESPRESSO data. This study adds to the growing body of literature employing GCMs to interpret high-resolution spectroscopic measurements of exoplanet atmospheres.