Dynamic spectrum of the Hα profile variation as a function of the orbital phase for RV Tau (top) and DF Cyg (bottom). The pulsations have been removed to better display the orbital motion. The phases in both plots correspond to phases in the spectroscopic orbits shown in Fig. 9. The plotted curve is the orbit of the primary. The vertical dashed lines represent the systemic velocity. The upper and lower horizontal dashed lines correspond to the superior and inferior conjunction, respectively, for RV Tau, and vice versa for DF Cyg.