DISKS AND JETS IN PLANETARY-NEBULAE

Highly collimated bipolar outflows and jets have been recently observe d to be associated with some planetary nebulae. Assuming that the mech anism of jet formation requires the presence of an accretion disk, we examine the possibilities to form such disks in the case of planetary nebulae with binary nuclei. We show that at the emergence from the com mon envelope phase, some systems can form accretion disks. Planetary n ebulae therefore form the newest addition to the classes of objects (w hich so far include active galactic nuclei, young stellar objects, and some X-ray binaries) which produce jets.