Projected line-of-sight velocity for the constant velocity profile. These are plotted over the normalised dynamic spectra of the Hα profile of BD+46°442 observed between BJD = 2 455 790 d and BJD = 2 456 000 d. The upper panel shows the observed spectra corrected for the photospheric contribution of the primary. The lower panel is the difference between the photospheric corrected spectra and a template spectrum taken at phase φ = 0.09, representing the variations in the strength of the absorption feature as a function of orbital phase. The continuum corresponds to a flux value of zero. Hence, absorption is represented by negative flux values and emission by positive values. The grey curves correspond to (full line), (dash-dotted line), and (dashed line).