Simulations of Evolving or Outbursting Molecular Protostellar Jets

The kinematic and radiative power of molecular jets is expected to change as a protostar undergoes permanent or episodal changes in the rate at which it accretes. We study here the consequences of evolving jet power on the spatial and velocity structure, as well as the fluxes, of molecular emission from the bipolar outflow. We consider a jet of rapidly increasing density and a jet in which the mass input is abruptly cut off. We perform three dimensional hydrodynamic simulations with atomic and molecular cooling and chemistry. In this work, highly collimated and sheared jets are assumed. We find that position-velocity diagrams, velocity-channel maps and the relative H$_2$ and CO fluxes are potentially the best indicators of the evolutionary stage. In particular, the velocity width of the CO lines may prove most reliable although the often-quoted mass-velocity power-law index is probably not. We demonstrate how the relative H$_2$ 1--0 S(1) and CO J=1--0 fluxes evolve and apply this to interpret the phase of several outflows.