He I absorption of HIP 67522b. (a) Mean full-transit and reference spectra, in 3 km s⁻¹ bins, versus vacuum wavelength in the stellar rest frame; gray: masked sky lines; dotted lines: He I wavelengths. (b) Spectra divided by the reference, in the planet rest frame, versus time from fourth contact; dashed lines: He I components; horizontal lines: third and fourth contacts; white: masked. (c) Ratio of the two spectra in (a), in 6 km s⁻¹ bins, with a Gaussian fit. (d) Excess EW of He I and of the Mg I control line (excluding a telluric H₂O line), per nodding pair.