Abstract
We present recent results of two topical problems on dynamical evolution of Planetary Nebulae (PNe) where binary nuclei, stellar rotation and magnetic fields play relevant roles. Namely, point-symmetry and multiple, collimated outflows. Firstly, for point-symmetric morphologies, MHD models considering a steady misalignment of the magnetic collimation axis with respect to the symmetry axis of the bipolar wind outflow are shown to successfully reproduce for the first time many of the morphologies that are observed. We compare the case of the bipolar PN Sa 2-237 with model results. Secondly, we discuss the origin of the extraordinary nebula KjPn 8. A substantial portion of the objects that go through the PN stage are expected to have binary nuclei, which may largely influence the stellar evolution process during and after the PN phase. Depending on the separation and mass ratio of the components, phenomena such as cataclysmic variables, symbiotic objects and novae may eventually be formed. In these cases, the mass ratios of the binary cores are far from unity and consequently the components evolve with widely different time scales. In contrast, ground-based multifrequency and HST observations indicate that in KjPn 8 we may be witnessing the case where two distinct and consecutive bipolar planetary nebulae-like events have been detected simultaneously, most probably originating from a binary core evolution with components of very similar mass having evolved nearly in parallel. In this case, KjPn 8 may be a rare object in our Galaxy and the first ever detected of this class.
