arXiv:astro-ph/9910022v1 1 Oct 1999 Asymmetrical Planetary Nebulae II: From Origins to Microstructures ASP Conference Series, Vol. XXX, 2000 J.H. Kastner, N. Soker, & S. Rappaport, eds. Searching for Jets in Asymmetrical Nebulae with the Hubble Space Telescope J. Patrick Harrington Department of Astronomy, University of Maryland, College Park, Maryland 20742 Kazimierz J. Borkowski Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 Abstract. The jets seen in NGC 6543 motivated us to search for sim- ilar features in other PNe. Our HST snapshot program looked for jets using the [N II] and Hα narrow-band filters. Although spectacular jets are found in proto-PNe, true jets seem rare among mature PNe. In the later group, IC 4593 is the best case in our sample. We distinguish be- tween jets and a number of interesting “jet-like” features, e.g., “cometary” structures with a dense globule at the end facing the central star. 1. Introduction Observations of Herbig-Haro objects like HH30 and HH34 have provided perhaps the best images of narrow, continuous jets. These jets are known to originate in the accretion disks surrounding the associated T-Tauri stars. Recently, morpho- logical studies of PNe have revealed many “point-symmetric” structures, which would have a natural explanation if the nebula were once subjected to the effects of precessing jets. But the existence of jets seems at variance with the conven- tional picture of the PN central star, which does not involve an accretion disk. In this context, any observations of jets in PNe, which provide a more direct indication of stellar accretion disks, are especially interesting. HST observations of NGC 6543 (the “Cat’s Eye Nebula”) confirmed the earlier indications (Miranda & Solf 1992) of a remarkable pair of jets in this object (Figure 1). We wanted to see if similar structures exist in other PNe. With this in mind, we carried out a “snapshot” imaging program of likely nebulae with the HST. 2. The HST Snapshot Program We selected our targets based on three criteria: (1) reports of high velocity flows (e.g., He 3-1475, the Eskimo), (2) point-symmetric morphologies, (3) ground- based images that showed “jet-like” structures. Since we found that in the case of NGC 6543 the jets were best seen in the ratio of the [N II] λ6584 to Hα filter images (Figure 1 is such a ratio image), we requested [N II] and Hα images 1