Theoretical mean absorption spectra between contact times T₂ and T₃ of the perfect overlap case computed with the out-of-transit spectrum, with and without sodium atmosphere as a function of the wavelength in the planetary rest frame. In addition to the simulations in Sect. 4.3, we included a day-to-nightside wind of 3 km s⁻¹ in the thermosphere. Upper panel: Zoom on the Na I D2 line. Lower panel: Zoom on the Na I D1 line.