We present results of a study of the proper motions of spectrally and kinematically separated structures in Herbig-Haro outflows with a new method which includes the measurements of the images, obtained with a scanning Fabry-Perot interferometer at two epochs, divided by 6-10 years or more. These observations were carried out mainly with the 6-meter telescope of the Special Astrophysical Observatory (SAO).
Comparison of Doppler images obtained in different epochs, corresponding to the same velocities, allows us to study the internal structures of flows, to trace their development and movement. As a final result, full 3D picture of the flows can be obtained.
The first observations with this technique were carried out in the field of HL/XZ Tau, where several jets and outflows were observed. Their morphological structures differed significantly in various radial velocities. The high-velocity structures were compact, while the low-velocity structures appeared as extended arc-like formations. However, the proper motion values of all structures with different radial velocities were found to be identical. Essentially, these structures represent the forward shock and reverse shock excitation region of the knots. In other words, the first ones correspond to the arc-like shock wave that excites the circumstellar medium, while the second ones represent the excited material within the jet itself. This result indicates that the knots in Herbig-Haro outflows are internal working surfaces formed as a result of episodic ejections of matter from the sources.
Using this approach, we studied other jets from young stars, such as HH 83, FS Tau B and PV Cep, where a similar effect was revealed.
