Shaping `Ears' in planetary nebulae by early jets
  We conduct three dimensional hydrodynamical numerical simulations of
planetary nebula (PN) shaping and show that jets that precede the ejection of
the main PN shell can form the morphological feature of ears. Ears are two
opposite protrusions from the main nebula that are smaller than the main nebula
and with a cross section that decreases monotonically from the base of an ear
at the shell to its far end. Only a very small fraction of PNe has ears. The
short-lived jets, about a year in the present simulations, interact with the
regular asymptotic giant branch (AGB) wind to form the ears, while the later
blown dense wind forms the main PN dense shell. Namely, the jets are older than
the main PN shell. We also find that for the jets to inflate ears they cannot
be too energetic, cannot be too wide, and cannot be too slow. A flow structure
where short-lived jets precede the main phase of nebula ejection by a few years
or less can result from a system that enters a common envelope evolution. The
low mass companion accretes mass through an accretion disk and launches jets
just before it enters the envelope of the giant progenitor star of the PN.
Shortly after that the companion enters the envelope and spirals-in to eject
the envelope that forms the main PN shell.
