  We discuss the interaction of the slow wind blown by an asymptotic giant
branch (AGB) star with a collimated fast wind (CFW) blown by its main sequence
or white dwarf companion, at orbital separations in the range of several AU to
about 200 AU. The CFW results from accretion of the AGB wind into an accretion
disk around the companion. The fast wind is collimated by the accretion disk.
We argue that such systems are the progenitors of bipolar planetary nebulae and
bipolar symbiotic nebulae with a very narrow equatorial waist between the two
polar lobes. We conduct a population synthesis study of the formation of
planetary nebulae in binary systems which quantitatively supports the proposed
model. We show the number of expected systems that blow a CFW is in accord with
the number found from observations, to within the many uncertainties involved.
Overall, we find that 5 per cent of all planetary nebulae are bipolars with
very narrow waists. Our population synthesis not only supports the CFW model,
but more generally supports the binary model for the formation of bipolar
planetary nebulae.
