Bipolar Planetary Nebulae from Outflow Collimation by Common Envelope
  Evolution
  The morphology of bipolar planetary nebulae (PNe) can be attributed to
interactions between a fast wind from the central engine and dense toroidal
shaped ejecta left over from common envelope (CE) evolution. Here we use the
3-D hydrodynamic AMR code AstroBEAR to study the possibility that bipolar PN
outflows can emerge collimated even from an uncollimated spherical wind in the
aftermath of a CE event. The output of a single CE simulation via the SPH code
PHANTOM serves as the initial conditions. Four cases of winds, all with high
enough momenta to account for observed high momenta preplanetary nebula
outflows, are injected spherically from the region of the CE binary remnant
into the ejecta. We compare cases with two different momenta and cases with no
radiative cooling versus application of optically thin emission via a cooling
curve to the outflow. Our simulations show that in all cases highly collimated
bipolar outflows result from deflection of the spherical wind via the
interaction with the CE ejecta. Significant asymmetries between the top and
bottom lobes are seen in all cases. The asymmetry is strongest for the lower
momentum case with radiative cooling. While real post CE winds may be
aspherical, our models show that collimation via "inertial confinement" will be
strong enough to create jet-like outflows even beginning with maximally
uncollimated drivers. Our simulations reveal detailed shock structures in the
shock focused inertial confinement (SFIC) model and develop a lens-shaped inner
shock that is a new feature of SFIC driven bipolar lobes.
