Irradiated and bent jets in the Orion Nebula

We present new images and proper-motion measurements of irradiated outflows from young stars in the outskirts of the Orion Nebula obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope. The images reveal many new outflows and new details in previously detected flows. The large-scale bipolar flows such as HH 502, 505, 874, and 876 contain multiple shocks whose velocities systematically decrease with increasing distance from their sources as the flows bend away from the core of the Orion Nebula. We consider several mechanisms for bending jets, including radiation pressure, the rocket effect on a neutral jet, and the impact of a side wind. While mild bends may be explained by either radiation pressure or the rocket effect, the extreme bends of some Orion jets and LL Ori-type bow shocks are best explained by the interaction of these outflows with a large-scale flow from the nebular core. The jet H alpha emission measures and geometry are used to estimate their mass-loss rates, which range from about. M similar to 10(-9) to 10(-6) M-circle dot yr(-1). Many of the quasi-parabolic bow shocks that wrap around young stars in Orion (the LL Ori-type objects) exhibit large gaps between the observed jets and the parabolic fronts facing the core of the nebula. These may indicate the additional action of a wide-angle outflow component such as a T Tauri stellar wind, a proplyd photoablation flow, or possibly a photoablation flow from the jet itself. The H alpha surface brightness and radii of the LL Ori fronts are used to estimate that the. MVw products of the wide-angle flow components have values around 10(-6) M-circle dot yr(-1) km s(-1). The side-wind density and velocity are also constrained. Outside the nebular core, the greatest concentration of bent jets and LL Ori-type parabolic fronts is located south and west of the Trapezium. The nonuniform, clumpy spatial distribution of jets, outflow sources, and proplyds in the outskirts of the Orion Nebula indicate that star formation occurred in small hierarchical clusters.