Proper motions of spectrally selected structures in the HH 83 outflow
  We continue our program of investigation of the proper motions of spectrally
separated structures in the Herbig-Haro outflows with the aid of Fabry-Perot
scanning interferometry. This work mainly focuses on the physical nature of
various structures in the jets. The aim of the present study is to measure the
proper motions of the previously discovered kinematically separated structures
in the working surface of the HH 83 collimated outflow. We used observations
from two epochs separated by 15 years, which were performed on the 6m telescope
with Fabry-Perot scanning interferometer. We obtained images corresponding to
different radial velocities for the two separate epochs, and used them to
measure proper motions. In the course of our data analysis, we discovered a
counter bow-shock of HH 83 flow with positive radial velocity, which makes this
flow a relatively symmetric bipolar system. The second epoch observations
confirm that the working surface of the flow is split into two structures with
an exceptionally large (250 km\ s$^{-1}$) difference in radial velocity. The
proper motions of these structures are almost equal, which suggests that they
are physically connected. The asymmetry of the bow shock and the turning of
proper motion vectors suggests a collision between the outflow and a dense
cloud. The profile of the H$\alpha$ line for the directly invisible infrared
source HH 83 IRS, obtained by integration of the data within the reflection
nebula, suggests it to be of P Cyg type with a broad absorption component
characteristic of the FU Ori like objects. If this object underwent an FU Ori
type outburst, which created the HH 83 working surfaces, its eruption took
place about 1500 years ago according to the kinematical age of the outflow.
