Internal velocities in the Orion nebula: large radial velocity features.
DOI T., O'DELL C.R. and HARTIGAN P.
Abstract (from CDS):
A map of high-velocity features in the 3'x5' central region of the Orion Nebula was created from slit spectra with a velocity resolution of 8 km/s. We identified two new bipolar flows, Herbig-Haro (HH) 725 and HH 726, as well as a highly redshifted flow, HH 512. We also found multiple new high-velocity co-moving features, all lying in the velocity range of -30 to -100 km/s. The newly discovered Big Arc appears as a slightly blueshifted feature. Unlike the other objects found, the Big Arc is not a shock; rather it is a result of a structural alteration in the nebula nearly extended across the sampled region. Spatial velocities of 19 features belonging to 11 HH objects were obtained by combining these radial velocity data with existing proper motion data. Most HH objects in the H II region exhibit spatial velocities ranging from 50 to 150 km/s. By analyzing their three-dimensional paths, HH 202 and HH 203+204 were found to be formed on the curved main ionization front, not on the Veil, as previously proposed. We have been able to locate the source of the HH 201 outflow (possibly the IRc2 feature within the BN/KL region) at 0.21 pc behind the ionization front of the nebula. This is in contrast to the Optical Outflow Source, which gives rise to most of the HH objects in the Orion Nebula and lies only a few hundredths of a parsec behind the ionization front of the nebula.