DEPROJECTION OF PLANETARY-NEBULA IMAGES

Several optical or radio images of planetary nebulae have been deproje cted using the algorithm described in Leahy & Volk [A&A (1993) (in pre ss)]. For each image 16 radial cuts from the center of the nebula were independently deprojected assuming either spherical symmetry or a wei ghting of the emissivity distribution towards the plane of the sky. Th e deprojection was carried out using the optical line images of Balick [AJ, 94, 671 (1987)] for the Ring Nebula (NGC 6720, PN G063.1+13.9) a nd NGC 40 (PN G120.0+09.8) and for the 15 GHz radio image of M3-35 (PN G071.6-02.3) from Aaquist & Kwok [ApJ, 378, 599 (1991)]. These three nebulae were chosen due to their generally ellipsoidal shapes as seen projected on the sky, but in all three cases the deprojection indicate s that the nebulae are neither oblate or prolate ellipsoidal shells. I nstead, these nebulae have two main regions of emission roughly opposi tely positioned around the central star each of which covers a solid a ngle of approximately pi steradians, and most of the emission is in mo re or less cylindrical bands with very little emissivity at the ''pole s'' of the nebulae. The nebulae are therefore more barrel-shaped than ellipsoid-shaped. While the possibility that planetary nebulae are cyl indrical in shape has been studied in the past, these results indicate that the body of the nebula is far more patchy than had been postulat ed which may resolve some of the difficulties that the hypothesis of c ylindrical symmetry has had. Such shapes are more complicated than the simplest form of the interacting winds model of planetary nebula form ation predicts, but can be explained if the progenitor red giant wind was rather asymmetrical.