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Session 50 - Molecular Outflows, Stellar Jets, and Herbig-Haro Objects.
Display session, Tuesday, January 14
Metropolitan Ballroom,
In this paper we explore the effect of radiative losses on hydrodynamic jet collimation models appropraite to Young Stellar Object (YSO). Building on a previous non-radiative study (Frank amp; Mellema 1996) we demonstrate that supersonic jets are a natural and robust consequence of wind-blown bubbles formed from central YSO winds interacting with aspherical environmental density distributions. Our new simulations show that the the addition of raditive cooling makes purely hydrodynamic jet collimation particularly effective. We find a number of of time-dependent processes can contribute to the collimation. The relative strengh of the different processes depends on the age of the system and the initial parameters characterizing the wind and environment. As predicted by Frank amp; Mellema 1996 we find that flow-focusing at an oblique inner shock becomes more effective when raditaive cooling is included. An unexpected feature of these simulations is the production of cool (T < 10^4 K), dense jets through the development of conical converging flows at the poles of the wind blown bubbles. For steady winds the formation of these jets occurs early in the evolution of the wind-blown bubbles. At later times we find the dynamical time scale for the jet material becomes comparible to its cooling time and the jet beam becomes hot (T \approx 10^6 K). The duration of the cool jet phase depends upon \dot M_w and V_w: the mass loss rate and velocity of the wind. High \dot M_w and low V_w produce longer cool jet phases.
