Do All PNe Come From Binaries?

We present a population synthesis calculation to derive the total number of planetary nebulae (PNe) in the Galaxy from single stars and binaries. By combining the most up-to-date literature results regarding galactic and stellar formation and evolution, we determined the total number of PNe with radii $<$0.8 pc deriving from single stars and binaries to be 46 000$±$15 000. By using common envelope (CE) calculations and observational results of main sequence binaries, we predict that 5 000$±$1 600 post-CE PNe with radii $<$0.8 pc exist in the Galaxy today. We compare these predictions with the observationally-based estimate of 7 200$±$1 800 PNe in the Galaxy with radii $<$0.8 pc. This suggests that many single stars do not produce PNe and that 69$±$28% of PNe we observe derive from CE interactions on the Asymptotic Giant Branch (AGB).