A POSSIBLE MECHANISM FOR WIGGLING PROTOSTELLAR JETS FROM 3-DIMENSIONAL SIMULATIONS IN A STRATIFIED AMBIENT MEDIUM

Most collimated supersonic protostellar jets show a collimated wigglin g, and knotty structure (e.g., the Hare 6-5B jet) and frequently revea l a long gap between this structure and the terminal bow shock. In a f ew cases, there is no evidence of such a terminal feature. We present three-dimensional smoothed particle hydrodynamical simulations that su ggest that this morphology may be due to the interaction of the propag ating cooling jet with a nonhomogeneous ambient medium. In regions whe re the ambient gas has an increasing density (and pressure) gradient, we find that it tends to compress the cold, low-pressure cocoon of sho cked material that surrounds the beam, destroy the bow shock-like stru cture at the head, and enhance beam focusing, wiggling, and internal t raveling shocks. In ambient regions of decreasing density (and pressur e), the flow widens and relaxes, becoming very faint. This could expla in ''invisible'' segments in systems like the Hare 6-5B jet. The bow s hock in these cases could be a relic of an earlier outflow episode, as previously suggested, or the place where the jet reappears after stri king a denser portion of the ambient medium.