Simulation‐based Investigation of a Model for the Interaction between Stellar Magnetospheres and Circumstellar Accretion Disks

We examine, parametrically, the interaction between the magnetosphere of arotating, young stellar object (YSO) and a circumstellar accretion disk using2.5-D (cylindrically symmetric) numerical magnetoydrodynamic simulations. Theinteraction drives a collimated outflow, and we find that the jet formationmechanism is robust. For variations in initial disk density of a factor of 16,variations of stellar dipole strength of a factor of 4, and for various initialconditions with respect to the disk truncation radius and the existence of adisk field, outflows with similar morphologies were consistently produced.Secondly, the system is self-regulating, where the outflow properties dependrelatively weakly on the parameters above. The large scale magnetic fieldstructure rapidly evolves to a configuration that removes angular momentum fromthe disk at a rate that depends most strongly on the field and weakly on therotation rate of the foot-points of the field in the disk and the mass outflowrate. Third, the simulated jets are episodic, with the timescale of jetoutbursts identical to the timescale of magnetically induced oscillations ofthe inner edge of the disk. To better understand the physics controlling thesedisk oscillations, we present a semi-analytical model and confirm that theoscillation period is set by the spin down rate of the disk inner edge.Finally, our simulations offer strong evidence that it is indeed theinteraction of the stellar magnetosphere with the disk, rather than someprimordial field in the disk itself, that is responsible for the formation ofjets from these systems.Comment: Accepted by ApJ; 34 pages, including 12 figures and 3 table