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 planet ary nebulae are analyzed in terms of the prolate ellipsoidal shell (PE S) 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 morphologica l classes. No significant differences can be found between the statist ics of morphological classes of high surface brightness/compact and lo w surface brightness/extended planetary nebulae, or with those classif ied by optical means. We conclude that the morphology of planetary neb ulae is determined early in their evolution. The degree of asymmetry p lanetary nebulae inherited from their asymptotic giant branch progenit ors is probably as important in determining the asymmetry observed in planetary nebulae as the shaping done by interacting winds during the planetary nebula phase.