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Kinematics of Optical Outflows in the Orion Nebula. I. The Giant Outflow HH 400 and the Irradiated Jet HH 502

We present narrowband filter and high-resolution, velocity-resolved Fabry-Perot images of outflows in the southern portion of the Orion Nebula. HH 400 is a giant, low-velocity, redshifted bow shock located about 10′ south of the core of the Orion Nebula. Its axis of symmetry passes close to the Trapezium cluster 1.5 pc to the north. The most likely point of origin is a young stellar object in the OMC-1 cloud core. HH 400 may be the remnant of a parsec-scale bipolar outflow powered by one of the young stars forming within this region. The radial velocity of gas in the limb-brightened rim of HH 400 is low, with redshifted speeds ranging from 8 to 20 km s-1 with respect to the emission from the Orion Nebula. The shape of the bow indicates that it lies close to the plane of the sky. For an inclination angle of 30° to the plane of the sky and assuming that the plasma is flowing mostly along the axis of symmetry, the visible gas at the rim of HH 400 has a mean velocity of about 30 km s-1, a mass of about 3 × 10-2 M⊙, and a dynamical age of about 5 × 104 yr, assuming the source lies in the OMC-1 cloud core. The estimated mass flux in the HH 400 bow is about 10-6 M⊙ yr-1. The bent bipolar irradiated jet HH 502 is superposed on the western rim of HH 400. We resolve the spatial and velocity structure of the jet and its multiple bow shocks. The jet consists of a chain of photoionized segments separated by wide gaps; bow shocks lie at the leading edges of these jet segments. The mean radial velocities of the jet segments decrease with increasing distance from the source. The large radial velocity dispersions of the gas at the tips of the HH 502 internal working surfaces and the small spreading angles of the HH 502 jet segments, combined with their low radial velocities, indicate that this flow lies close to the plane of the sky. Assuming that the jet is fully ionized, that it spreads at the Mach angle, and that the internal sound speed in the photoionized gas is about 10 km s-1, the jet must have a space velocity of about 400 km s-1. Finally, we present velocity-resolved images of the bow shocks in HH 540, a flow that may originate from the large protoplanetary disk 181-826. Several additional high-velocity features identified in the Fabry-Perot data trace additional jets and outflows in this portion of the Orion Nebula.