Map of differential profiles during HD 209458b epoch 1, in the region of the sodium doublet. Values are colored as a function of flux and plotted as a function of wavelengths in the star rest frame (in abscissa) and orbital phase (in ordinate). The planet-occulted stellar lines of sodium and nickel are clearly visible during transit (contacts are shown as white dashed lines). Visual inspection of out-of-transit and in-transit continuum values do not show any strong systematic features.