Planetary nebula progenitors that swallow binary systems

Abstract

I propose that some irregular 'messy' planetary nebulae owe their morphologies to triple-stellar evolution where tight binary systems evolve inside and/or on the outskirts the envelope of asymptotic giant branch (AGB) stars. In some cases the tight binary system can survive, in other it is destroyed. The tight binary system might breakup with one star leaving the system. In an alternative evolution, one of the stars of the brook-up tight binary system falls toward the AGB envelope with low specific angular momentum, and drowns in the envelope. In a different type of destruction process the drag inside the AGB envelope causes the tight binary system to merge. This releases gravitational energy within the AGB envelope, leading to a very asymmetrical envelope ejection, with an irregular and 'messy' planetary nebula as a descendant. The evolution of the triple-stellar system can be in a full common envelope evolution (CEE) or in a grazing envelope evolution (GEE). Both before and after destruction (if take place) the system might lunch pairs of opposite jets. One pronounced signature of triple-stellar evolution might be a large departure from axisymmetrical morphology of the descendant planetary nebula. I estimate that about one in eight non-spherical PNe is shaped by one of these triple-stellar evolutionary routes.