Transmission spectra ($T_{\lambda ,\text{i}}={\text{F}}_{\text{i}}\left(\tilde{\lambda }\right)/{\text{S}}_{\text{out}}\left(\lambda \right)-1$) shown in tomography in the planetary rest frame in the region of the He I triplet, as a function of wavelength and planetary orbital phase (left). The contact points t₁, t₂, t₃, and t₄ are marked with horizontal black lines. The regions affected by OH⁻ contamination are masked. Mean-transmission spectrum for each observed transit (right). The horizontal blue line is the white-light radius (R_pl/R_⋆)². The mean transmission spectra have an inverted sign compared to ${\text{F}}_{\text{i}}\left(\tilde{\lambda }\right)/{\text{S}}_{\text{out}}\left(\lambda \right)-1$ as the radius is expressed instead of absorption. Black vertical lines indicate the position of the He I lines. Red line marks the spectral regions affected by OH⁻ emission. For some planets, some residuals are left at the position of the Si line (~1083 nm). This is due to the depth of the line which can give rise to difficulties in the spectral extraction (see e.g., Krishnamurthy et al. 2023).