FORMATION OF BIPOLAR PLANETARY NEBULAE BY INTERMEDIATE-LUMINOSITY OPTICAL TRANSIENTS

We present surprising similarities between some bipolar planetary nebulae (PNe) and eruptive objects with peak luminosity between novae and supernovae. The latter group is termed ILOT for intermediate-luminosity optical transients (other terms are intermediate-luminosity red transients and red novae). In particular, we compare the PN, NGC 6302 and the pre-PNe OH231.8+4.2, M1-92, and IRAS 22036+5306 with the ILOT NGC 300 OT2008-1. These similarities lead us to propose that the lobes of some (but not all) PNe and pre-PNe were formed in an ILOT event (or several close sub-events). We suggest that in both types of objects the several months long outbursts are powered by mass accretion onto a main-sequence (MS) companion from an asymptotic giant branch (AGB, or extreme-AGB) star. Jets launched by an accretion disk around the MS companion shape the bipolar lobes. Some of the predictions that result from our comparison is that the ejecta of some ILOTs will have morphologies similar to those of bipolar PNe, and that the central stars of the PNe that were shaped by ILOTs should have an MS binary companion with an eccentric orbit of several years long period.