Multiple emission line components in detached post-common-envelope binaries (Research Note)

Motivated by the recent discovery of an Hα emission line component originating close to the white dwarf primary in the post-commonenvelope binary (PCEB) LTT 560, we have undertaken a spectroscopic snapshot survey on 11 short-period (Porb < 6 h) PCEBs using FORS2. We have found multi-component Hα emission line profiles in six of our targets, indicating that multiple Hα emission sites are rather common in short-period PCEBs. The underlying physical mechanisms, however, can be fundamentally different. In our sample we find one system where the extracted radial velocities of two identified components indicate that both originate in the late-type secondary star, where one is caused by irradiation from the hot white dwarf primary and the other by stellar activity. Another object presents two components that are located on opposite sides of the centre-of-mass, suggesting a case similar to LTT 560, i.e. that accretion of stellar wind from the secondary star produces Hα emission on, or close to, the white dwarf.