First detection of acceleration and deceleration in protostellar jets?
  Time variability in the Cha II outflows
  We present a multi-epoch (20 years baseline) kinematical investigation of
HH52, 53, and 54 at optical and near-IR wavelengths, along with medium and
high- resolution spectroscopic analyses, probing the kinematical and physical
time variability conditions of the gas along the flows. By means of multi-epoch
and multi-wavelength narrow-band images, we derived proper motions, tangential
velocities, velocity and flux variability of the knots. Radial velocities and
physical parameters of the gas were derived from spectroscopy. Finally, spatial
velocities and inclination of the flows were obtained by combining both imaging
and spectroscopy. The P.M. analysis reveals three distinct, partially
overlapping outflows. In 20 years, about 60% of the knots show some degree of
flux variability. Our set of observations apparently indicates acceleration and
deceleration in a variety of knots along the jets. For about 20% of the knots,
mostly coincident with working surfaces or interacting knots along the flows, a
relevant variability in both flux and velocity is observed. We argue that both
variabilities are related and that all or part of the kinetic energy lost by
the interacting knots is successively radiated. The analysis indicates the
presence of very light, ionised, and hot flows, impacting a denser medium.
Several knots are deflected. At least for a couple of them (HH54 G and G0), the
deflection originates from the collision of the two. For the more massive parts
of the flow, the deflection is likely the result of the flow collision with a
dense cloud or with clumps.
