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Chin-Fei Lee, J. M. Stone, E. C. Ostriker, L. G. Mundy (UMD)
We present a comprehensive survey of two-dimensional hydrodynamical simulations of both jet- and wind-driven models of protostellar outflows in order to test which provides a better fit to the kinematics of observed molecular outflows. In simulations of steady jets, swept-up ambient gas forms a thin shell that might be detected as a molecular outflow. We find a simple ballistic bow-shock model is able to reproduce the structure and transverse velocity of the shell. Position-velocity (PV) diagrams for the shell cut along the outflow axis show a convex spur structure with the highest velocity at the bow tip. The power-law index of the mass-velocity relationship ranges from 1.5 to 3.5, depending strongly on the inclination. If the jet is time-variable, the PV diagrams show multiple convex spur structures and the power-law index becomes smaller than the steady jet simulation. In simulations of isothermal steady wide-angle winds, we find the structure and kinematics of the swept-up shell is well described by a momentum-driven shell model. In contrast to the jet simulations, the PV diagrams for the shell cut along the outflow axis show a lobe structure tilted with inclination. The power-law index of the mass-velocity relationship ranges from 1.3 to 1.8. If the wind is time-variable, the PV diagrams also show multiple structures, and the power-law index becomes smaller than the steady wind simulation. Comparing the different simulations with observations, we found that some outflows, e.g., HH 212, show features consistent with the jet-driven model, while others, e.g., VLA 05487, are consistent with the wind-driven model.