On the matter entrainment by stellar jets and the acceleration of molecular outflows

We study, by numerical simulations, the entrainment process in a supersonic , radiative jet flow, during the evolution of Kelvin-Helmholtz instabilitie s, in the context of the the acceleration problem of molecular bipolar outf lows observed in Giant Molecular Clouds. Our results show that a large frac tion of the initial jet momentum can be transferred to the ambient medium b y this process. We therefore analyze in detail the instability evolution an d compare some of the main observational properties of molecular outflows w ith those of the entrained material that we observe in our simulations. In particular, we find a good agreement for the mass vs. velocity distribution and for the outflow collimation structure, especially when a light jet is moving into a denser ambient medium. This is probably the case for (obscure d) optical jets driving powerful molecular outflows in the denser environme nt of the inner regions of molecular clouds.