H_α emission lines of AK For. In a given panel, all spectra were continuum-fitted and equally scaled. The dashed lines show the level of continuum and mark the orbital phase or time of the observation. Top: all spectra are shown as a function of the orbital phase. Solid blue lines trace the position of the H_α line as predicted by the orbital solution. Bottom: three FEROS spectra from March 2013, which show rapid evolution of the H_α profiles. On March 30, the emission was much stronger than a few days earlier. Secondary’s emission is the stronger one.