The time evolution of the stellar spectra occulted by the planet as a function of orbital phase, in the wavelength range 5882-5902 Å, which includes the sodium doublet. The positions of the Na I lines are highlighted by vertical dotted lines. The horizontal white lines indicate the transit contacts, with solid white representing T1 and T4, and dashed gray representing T2 and T3 (from negative to positive values of phase). This map was constructed by subtracting the in-transit flux-weighted spectra from a reference out-of-transit spectrum.