One-sided outflows/jets from rotating stars with complex magnetic fields

Abstract

We present for the first time axisymmetric magnetohydrodynamic simulations which show the formation of intrinsically asymmetric or one-sided outflows or jets from disc accretion on to a rotating star with a complex magnetic field. The intrinsic magnetic field of the star is assumed to consist of a superposition of an aligned dipole and an aligned quadrupole in different proportions. The star is assumed to be rapidly rotating in the sense that the star's magnetosphere is in the propeller regime where strong outflows occur. Our simulations show that for conditions where there is a significant quadrupole component in addition to the dipole component, then a dominantly one-sided conical wind tends to form on the side of the equatorial plane with the larger value of the intrinsic axial magnetic field at a given distance. For cases where the quadrupole component is absent or very small, we find that dominantly one-sided outflows also form, but the direction of the flow 'flip-flops' between upward and downward on a time-scale of ~30 d for a protostar. The average outflow will thus be symmetrical. In the case of a pure quadrupole field we find symmetric outflows in the upward and downward directions. © 2010 The Authors. Journal compilation © 2010 RAS.