http://arxiv.org/abs/1507.08702
We model the generation of a magnetic field in a protostellar disc using an \alpha-dynamo and perform axisymmetric magnetohydrodynamics (MHD) simulations of a T Tauri star. We find that for small values of the dimensionless dynamo parameter $\alpha_d$ the poloidal field grows exponentially at a rate ${\sigma} \propto {\Omega}_K \sqrt{\alpha_d}$ , before saturating to a value $\propto \sqrt{\alpha_d}$ . The dynamo excites dipole and octupole modes, but quadrupole modes are suppressed, because of the symmetries of the seed field. Initial seed fields too weak to launch MHD outflows are found to grow sufficiently to launch winds with observationally relevant mass fluxes of order $10^{-9} M_{\odot}/\rm{yr}$ for T Tauri stars. For large values of $\alpha_d$ magnetic loops are generated over the entire disc. These quickly come to dominate the disc dynamics and cause the disc to break up due to the magnetic pressure.
S. Dyda, R. Lovelace, G. Ustyugova, et. al.
Mon, 3 Aug 15
22/43
Comments: 15 pages, 13 figures
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