Origin of planetary nebulae - Morphology, carbon-to-oxygen abundance ratios, and central star multiplicity

The authors have examined data pertaining to the morphology, carbon-to-oxygen abundance ratio, and central star multiplicity of 139 planetary nebulae (PNs). Among 108 nonstellar PNs, ≡50% display a bipolar symmetry, and an additional ≡30% display elliptical symmetry. Comparison of the sizes of extreme red giant stars and separations of main-sequence, solar-type binary stars suggests that the gravitational field of a companion star is unlikely to be responsible for the mass ejection in all or even a majority of these cases. However, it is perhaps conceivable that a secondary star is responsible for most of the above-mentioned symmetries. Based on optical, ultraviolet, infrared, and radio data, the authors find 42 C-rich and 26 O-rich PNs in the set. These numbers agree with the relative numbers of C- and O-rich red giant stars with large mass loss rates and are consistent with the idea that the progenitors of PNs are this class of red giant stars.