SUCCESSIVE SIO SHOCKS ALONG THE L-1448 JET AXIS

We present a complete SiO v = 0 J = 2 --> 1 synthesis image of the red -shifted outflow lobe from the Class 0 protostar L 1448-mm. The image is a 5-field mosaic obtained with the IRAM interferometer at similar t o 3 '' angular resolution. The SiO emission arises in a highly-collima ted jet extending over 0.2 pc. The jet consists of four main blobs, pr obably corresponding to successive episodes of mass-loss from the cent ral object. The kinematical structure of the jet is studied by the mea ns of velocity channel maps and position-velocity diagrams, and is com pared to current models of jet-driven bipolar outflows. We have constr ucted a kinematical model of bow-shock to make such comparison as deta iled as possible. We find that most of the SiO clumps delineate partia l bow-shock structures, but important SiO emission is also seen along the jet axis itself. Shock-processing of the dust grains, and perhaps chemical gas-phase reactions in the protostellar wind and in the mixin g layer, could explain the enhancement of SiO in the different jet blo bs. The CO outflow in L1448, and perhaps in all bipolar outflows, is t hought to be driven by a primary jet ejected from the central star/dis k system. We conclude that, if not the primary wind itself, the materi al traced by the SiO emission reported here is very closely linked to this primary jet.