http://arxiv.org/abs/1502.01357
A large set of 2.5D MHD simulations has been carried out for axisymmetric viscous/diffusive disc accretion to rotating magnetized stars for the purpose of assessing the conditions where the outflows or jets are asymmetric relative to the equatorial plane. Observations of jets from young stellar objects reveal the asymmetric outflows from some sources. The considered initial magnetic fields are symmetric about the equatorial plane and consist of a radially distributed field threading the disc (disc-field) and a stellar dipole field. (1). For pure disc-fields the symmetry or asymmetry of the outflows is affected by the midplane plasma $\beta$ of the disc. For the low density discs with small plasma $\beta$ values, outflows are observed to be symmetric about the equatorial plane to within 10% over timescales of hundreds of inner disc orbits. For the denser higher $\beta$ discs, the coupling of the upper and lower coronal plasmas is broken, and quasi-periodic field motion in the two hemispheres becomes different. This asymmetry leads to asymmetric episodic outflows. (2.) Accreting stars with a stellar dipole field and no disc-field exhibit episodic, two component outflows – a magnetospheric wind and an inner disc wind from somewhat larger radial distances. Both are characterized by similar velocity profiles but the magnetospheric wind has densities 10 times that of the disc wind. The winds are highly asymmetric with outflow from one hemisphere and funnel flow accretion in the opposite hemisphere. (3.) Adding a disc-field which is anti-parallel to the stellar dipole field in the disc acts to suppress the magnetospheric and disc winds. In contrast, adding a disc-field parallel to the stellar dipole field acts to enhance the episodic magnetospheric and disc winds. The winds are again highly asymmetric about the equatorial plane. They are not influenced by the initial plasma $\beta$ of the disc.
S. Dyda, R. Lovelace, G. Ustyugova, et. al.
Fri, 6 Feb 15
23/59
Comments: 16 pages, 18 figures
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