2019MNRAS.483.5020S

I propose that at the termination of the common envelope evolution (CEE) the companion to the giant star might launch jets that have variable directions and intensities, hence the jets shape the inner zones of the descendant nebula causing it to lose any type of symmetry. This might account for some of the chaotic departures from axisymmetric structures in some planetary nebulae. I base my study on the assumption that at the termination of the CEE the binary interaction forms a circumbinary thick disc that feeds the companion via an accretion disc that launches opposite jets. I consider two processes that might lead to the development of Rayleigh-Taylor instabilities that lead to chaotic accretion flow on to the companion. The chaotic accretion flow leads to a variable accretion disc around the companion, hence to variable jets. In the first process the jets inflate low-density hot bubbles in the inner regions of the envelope. In the second process the inner boundary of the thick circumbinary disc, that faces the centre, cools by radiation thus leading to a temperature, and hence also a pressure, increase with radius. The opposite pressure and density gradients lead to Rayleigh-Taylor instabilities. This study further underlines the importance of exploring the termination phase of the CEE to the understanding of the entire CEE and its outcomes.