EFFECTS OF COOLING ON THE PROPAGATION OF MAGNETIZED JETS

We present multidimensional simulations of magnetized radiative jets a ppropriate to young stellar objects (YSOs). Magnetized jets subject to collisionally excited radiative losses have not, as yet, received ext ensive scrutiny. The purpose of this Letter is to articulate the propa gation dynamics of radiative MHD jets in the context of the extensive jet literature. Most importantly, we look for morphological and kinema tic diagnostics that may distinguish hydrodynamic protostellar jets fr om their magnetically dominated cousins. Our simulations are axisymmet ric (2.5 dimensions). A toroidal (B-phi) field geometry is used. Our m odels have high sonic Mach numbers (M-f approximate to 10) but lower f ast-mode Mach number (M-f approximate to 5). This is approximately the case for jets formed via disk-wind or X-wind models-currently the con sensus choice for launching and collimating YSO jets. Time-dependent r adiative losses are included via a coronal cooling curve. Our results demonstrate that the morphology and propagation characteristics of str ongly magnetized radiative jets can differ significantly from jets wit h weak fields. In particular, the formation of nose cones via postshoc k hoop stresses leads to narrow bow shocks and enhanced bow shock spee ds. In addition, the hoop stresses produce strong shocks in the jet be am, which contrasts with the relatively unperturbed beam in radiative hydrodynamic jets. Our simulations show that pinch modes produced by m agnetic tension can strongly affect magnetized protostellar jets. Thes e differences may be useful in observational studies designed to disti nguish between competing jet collimation scenarios.