  The driving mechanism of jets and outflows in star formation process is
studied using resistive MHD nested grid simulations. We calculated cloud
evolution from the molecular cloud core to the stellar core. In the collapsing
cloud core, we found two distinct flows: Low-velocity flows (sim 5 km/s) with a
wide opening angle, driven from the adiabatic core, and high-velocity flows
(sim 30 km/s) with good collimation, driven from the protostar. High-velocity
flows are enclosed by low-velocity flows after protostar formation. The
difference in the degree of collimation between the two flows is caused by the
strength of the magnetic field and configuration of the magnetic field lines.
The magnetic field around an adiabatic core is strong and has an hourglass
configuration; therefore, flows from the adiabatic core are driven mainly by
the magnetocentrifugal mechanism and guided by the hourglass-like field lines.
In contrast, the magnetic field around the protostar is weak and has a straight
configuration owing to Ohmic dissipation in the high-density gas region.
Therefore, flows from the protostar are driven mainly by the magnetic pressure
gradient force and guided by straight field lines. Differing depth of the
gravitational potential between the adiabatic core and the protostar cause the
difference of the flow speed. Low-velocity flows correspond to the observed
molecular outflows, while high-velocity flows correspond to the observed
optical jets. We suggest that the outflow and the jet are driven by different
cores, rather than that the outflow being entrained by the jet.
