HD 209458 b low-resolution (ℛ ≈ 500) transit depth and species contributions simulated with Exo-REM. The grey areas represent the wavelength range of the CRIRES+ orders. On top are indicated the orders index number. From top to bottom: models with a C/O ratio of 0.1, 0.55, and 0.8, respectively. Dotted: the combined contributions of the H₂−H₂ and H₂−He collision-induced absorptions and the effect of Rayleigh scattering. Dashed: the total contribution of the SiO₂, Mg₂SiO₃ and Fe clouds for a cloud coverage of 1.0. The contributions of CO₂, FeH, K, Na, PH₃, TiO and VO were negligible in this spectral region and thus are not represented.