Herbig-Haro flows in 3D: The HH83 jet

Aims. The kinematics of the HH83 optical outflow, located in the L 1641 molecular cloud, are investigated. Methods. Observations were carried out with the Fabry-Perot scanning interferometer on the 6-m telescope of the Special Astrophysical Observatory. The H? emission line was scanned with a spectral resolution of R = 8200. Results. The radial velocity along the jet increases with distance from the source, confirming previous results. It also shows lower amplitude variations which are not correlated with intensity. Both the spatial width of the jet as well as the FWHM of the H? emission line in the jet tend to decrease with distance from the source. The velocity field across the jet demonstrates a decrease from the center to the edges as well as some evidence for a transverse velocity gradient. The blue-shifted bow shock is separated spatially and spectrally into two distinct features, divided by about 2? and 250 km s -1, accordingly. Conclusions. Evidence is provided that these split features correspond to forward and reverse shocks caused by a rapid pressure increase as the jet begins a new oblique impact on the surrounding medium. Radial velocity variations lengthwise and transverse to the jet axis are discussed. Linear extrapolation of the jet velocity up to the location of the terminal shock region yields the radial velocity of the reverse jet shock. The data are consistent with an abrupt outburst about one thousand years ago which ejected material with total speeds of up to 400 kms -1.