Binarity and symbiotics in asymmetrical Planetary Nebulae

We show that there are strong links between certain types of asymmetrical Planetary Nebulae (PNe) and symbiotic stars. Symbiotics are binaries and several have extended optical nebulae all of which are asymmetrical and greater than or equal to 40% are bipolar. Bipolar PNe are likely to be formed by binaries and share many properties with symbiotic nebulae (SyNe). Some PNe show point symmetry which is naturally explained by precession in a binary system. M2-9 has both point and plane symmetry, and has been shown to have a binary central object. We show that inclination on the sky affects the observed properties of bipolar nebulae due to enhanced equatorial densities, and compare observations of a sample of BPNe with a simple model. Good agreement is obtained between model predicted and observed IR/optical flux ratios and apparent luminosities, which further confirms the binary hypothesis.