Hα line of BD+46°442 at two different phases in the orbital period. The Hα line displays a double-peaked emission feature with a central absorption feature during inferior conjunction (black solid line), when the post-AGB star is between the jet and the observer. During superior conjunction, when the jet is between the post-AGB star and the observer, we observe a blue-shifted absorption feature in the Hα line (blue dotted line).