Multiple emission line components in detached post-common-envelope binaries

TL;DR

This study reveals that multiple Halpha emission components are common in short-period post-common-envelope binaries, originating from different physical mechanisms such as stellar activity, irradiation, or accretion.

Contribution

The paper provides the first spectroscopic survey showing multi-component Halpha emission in short-period PCEBs and identifies their possible physical origins.

Findings

Six out of eleven PCEBs show multi-component Halpha emission.

Different physical mechanisms cause the multiple emission components.

Evidence of stellar wind accretion onto white dwarfs in some systems.

Abstract

Motivated by the recent discovery of an Halpha emission line component originating close to the white dwarf primary in the post-common-envelope binary (PCEB) LTT 560, we have undertaken a spectroscopic snapshot survey on 11 short-period (P_orb < 6 h) PCEBs using FORS2. We have found multi-component Halpha emission line profiles in six of our targets, indicating that multiple Halpha 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 Halpha emission on, or close to, the white dwarf.