Dynamical spectra in the neighbourhood of the Hα profile in a grey-scale representation created in the program phdia. Left-hand panel: observed spectra; right-hand panel: difference spectra after the subtraction of a synthetic spectrum (including the Hα profile) of star 2. The phases shown on both sides of the figure, correspond to ephemeris (3). The spectra are repeated over two orbital cycles to show the continuity of the orbital phase changes.