Radio morphologies of planetary nebulae

We have examined the morphologies of planetary nebulae observed in the recent very large array (VLA) surveys. The high angular resolution of the VLA has allowed the extension of morphological classification to a much more compact population than before. The radio images of planetary nebulae are analyzed in terms of the prolate ellipsoidal shell (PES) model. Simulated radio images are produced using various asymmetry parameters in the PES model. Using these models as a guide, the radio images of planetary nebulae are classified into different morphological classes. No significant differences can be found between the statistics of morphological classes of high surface brightness/compact and low surface brightness/extended planetary nebulae, or with those classified by optical means. We conclude that the morphology of planetary nebulae is determined early in their evolution. The degree of asymmetry planetary nebulae inherited from their asymptotic giant branch progenitors is probably as important in determining the asymmetry observed in planetary nebulae as the shaping done by interacting winds during the planetary nebula phase.