Residual maps and transmission spectra around the He I triplet lines for the corrected (left column) and masked (right column) procedures. Top panels: residual maps in the stellar rest frame. Middle panels: residual maps in the planet rest frame. Planet orbital phase is shown in the vertical axis, wavelength is in the horizontal axis, and relative absorption is colour-coded. Dashed white horizontal lines indicate the first (T1) and fourth (T4) contacts. Cyan lines show the theoretical trace of the planetary signals. Bottom panels: transmission spectra obtained around an He I triplet, combining all the spectra between T1 and T4. We show the original data in light grey and the data binned by 0.2 Å in black. Cyan vertical lines indicate the He I triplet lines’ positions. Best Gaussian fit model is shown in red along with its 1σ uncertainties (shaded red region). Residuals after subtracting the best fit model are shown below. All the wavelengths in this figure are referenced in the vacuum.