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Astron. Astrophys. 343, 571-584 (1999)

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6. Conclusion

The [FORMULA] angular resolution images of HH 211 presented in this paper reveal the internal structure, at a [FORMULA] AU scale, of an extremely young molecular outflow. The wealth of information provided by mm-wave interferometry allows detailed studies of the morphology and kinematics of the different parts (protostellar condensation, jet, shocks, cavities) of the flow. Our main conclusions are the following:

  • The exciting source of the HH 211 molecular outflow is a (presumably Class 0) low-mass protostar surrounded by a [FORMULA] dust condensation which is elongated in a direction roughly perpendicular to the jet/flow axis.

  • The low-velocity CO emission reveals the cavities of the two lobes of the outflow. Despite some obvious perturbations of the flow due to interactions with the ambient medium, the shape of the eastern, blueshifted lobe is extremely regular and allows direct comparison with predictions from simulations. Its morphology can actually be (surprisingly well) reproduced by a very simple, semi-analytical toy-model of the propagation of a bow-shock.

  • The high-velocity CO emission traces an extremely collimated jet-like structure, located on the axis of the low-velocity CO cavities, with a linear apparent acceleration with distance from the protostar. This CO "jet" may correspond to a dense cocoon, entrained along the sides of the underlying jet and/or made by the wakes of several small bowshocks created by internal working surfaces within the jet. The estimated jet mass and mass loss rate yield a timescale of order one thousand years, in good agreement with the kinematical age.

  • The HH 211 molecular outflow appears as a prime test-case for the jet-driven outflow paradigm: its overall structure, including a flattened protostellar envelope, a protostellar jet, bow-shocks at the extremity of the jet and low-velocity cavities in the wake of these shocks, perfectly fits into the prediction of this model. Hence, our observations strongly supports prompt entrainment at the head of a travelling bow-shock as the formation mechanism of young, embedded molecular outflows.

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999