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 ∼3′′ angular resolution. The SiO emission arises in a highly-collimated jet extending over 0.2 pc. The jet consists of fourmain blobs, probably corresponding to successive episodes of mass-loss from the central object. The kinematical structure of the jet is studied by the means of velocity channel maps and position-velocity diagrams, and is compared to current models of jet-driven bipolar outflows. We have constructed a kinematical model of bow-shock to make such comparison as detailed as possible. We find that most of the SiO clumps delineate partial bow-shock structures, but important SiO emission is also seen along the jet axis itself. Shockprocessing of the dust grains, and perhaps chemical gas-phase reactions in the protostellar wind and in the mixing layer, could explain the enhancement of SiO in the different jet blobs. The CO outflow in L1448, and perhaps in all bipolar outflows, is thought to be driven by a primary jet ejected from the central star/disk system. We conclude that, if not the primary wind itself, the material traced by the SiO emission reported here is very closely linked to this primary jet.