Properties of the Na I D lines of WASP–12. Top panel: Na I D₂ line of WASP–12 (solid blue) along with spectrum reflected at nominal wavelength of the line (red dashed). Bottom panel: ratio between original and reflected spectrum for Na I D₁ and Na I D₂ lines (solid magenta and black) along with best-fit model (dashed magenta and black). The green shade indicates the considered fit range.