Excess absorption spectra with thermospheric sodium, as a function of wavelength in the stellar rest frame, computed with the different reference spectra mentioned in Sect. 3.1 and for a v_eq sin(i) = 3 km s⁻¹. Upper panels: excess absorption spectra. Lower panels: quantities used to compute the absorption spectra. Here, F_out was multiplied by the ratio between the occulted surface and the surface of the star to bring it to the level of F_loc and make the comparison easier. We show results for different time-steps (T₂ and T₀) and sky-projected spin-orbit angles (0 and 45^°).