The Shaping of Planetary Nebulae

CCD images of planetary nebulae in various emission lines have been obtained for about 50 northern objects. The signatures of snowplows driven by a hot bubble interior are nearly ubiquitous in the sample. The geometry of the bubble-nebula interface argues that mass ejection prior to the hot wind phase is densest in an equatorial plane. The interface is delineated best in emission lines ranging in ionization from high (He⁺⁺) to low (N⁺ and occasionally O⁰). A very preliminary analysis suggests that some of the heating in the snowplows arises from a source other than stellar UV radiation.