The HH flow associated with young stellar object HL Tau has an exciting
history and even until now the origin of some its features is not clear yet.
Flow starts as the relatively faint and narrow jet from HL Tau
but at distance of about 20" from the star it abruptly changes direction
by about 14 deg and becomes much brighter and appears complex knotty
morphology. Knotty structures of Herbig-Haro jets are common phenomena
and knowing the origin of such structures is essential for understanding
the processes of jet formation. Basically, there are two theoretical
approaches: different types of instabilities in stationary flow, and
episodic ejection of the matter.
Contact - Tigran Movsessian
The first scanning Fabry-Perot interferometry of HL Tau jet revealed
the complex kinematical structure
et al., 2007) in the jet. In the flow detected compact knots with
high (-150 km/s) and bow shape structures in front of those, with low radial
velocities (-50 km/s). To study the origin of those structures it is
important to have not only radial velocities but tangential velocities
also, by the use of proper motion. We use two epoch (2001, 2007) scanning
Fabry-Perot observations obtained with
focal reducer at SAO RAS 6-m telescope to measure proper motions of
the structures with various radial velocities. The most interesting result
is that the structural components with low and high radial velocity both
have very similar values of tangential velocity nearly 160 km/s.
This result witnesses to the formation of high and low velocity structures
in the HL Tau jet formed by episodic ejection of the matter. In this case
we observe emission of high velocity clump of gas and bow shape supersonic
wave in front of it. Increase of relative surface brightness of bow-shocks
could be the result of abrupt change of the physical conditions of the
ambient medium as well as the interaction of a highly collimated flow and
the side wind from XZ Tau.
Movsessian T.A., Magakyan T.Yu., Moiseev A.V.,
2012, A&A, 541, A16;