Transmission spectra shown in tomography in the planetary (left) and stellar (right) rest frame, as a function of the wavelength and the orbital phase (transmission spectra are binned both in wavelength and in phase). An excess absorption (in blue) is present during the transit, the three helium triplet lines are indicated with vertical black lines. The contact point t₁, t₂, t₃ and t₄ are marked with horizontal white lines.