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Item Open Access The role of MHD instabilities in the magnetospheric propeller outflow and emission in the nova-like variable star AE Aquarii(University of the Free State, 2007-02) Venter, Louis Albert; Meintjes, P. J.English: AE Aquarii is a close binary consisting of a white dwarf primary star and a K4-5 red dwarf, the secondary. Mass is transferred from the Roche lobe filling secondary to the Roche lobe of the white dwarf. The white dwarf has a spin period Pspin 33 s and a fast corotating magnetosphere. The trajectory of the flow brings it to a closest approach rcl 1010 cm which is outside the corotation radius. Observational studies of the emisssion lines, in conjuction with the observed spin-down of the white dwarf, suggests that the bulk of the mass transfer is propelled from the system. The ejection of the flow is proposed to result from the interaction of the mass flow with the fast rotating magnetosphere. The interaction transfers angular momentum from the magnetosphere to the mass flow. The unique contribution of this study lies therein that this plasma-magnetosphere interaction is modelled as being driven by the Kelvin-Helmholtz (KH) instability, which is assumed to grow at the interface between the mass flow and the magnetosphere. The process can be quantified by evaluating the Poynting flux S, of the magnetospheric field at the radius of closest approach. The energy dissipation rate of the field across the surface of the stream A is PMHD = S x A 1034 erg s−1. Furthermore, if the mass transfer is ejected by the propeller at the escape velocity vesc 1550 km s−1, the energy carried by the outflow is Pout = 12 ˙M v2 esc 5 × 1033 erg s−1, where ˙M is the mass transfer rate. It is therefore plausible that the magnetospheric propeller is responsible for the ejection of the mass transfer. The ultimate energy source for the propeller is the spin of the white dwarf which has been shown to be losing rotational kinetic energy at the rate Pspin 1034 erg s−1. The KH driven magnetospheric propeller also results in the formation of magnetized plasmoids of energized electrons that emit synchrotron emission between infra-red and 1GHz radio frequencies as they are ejected from the system and expand. A large diffuse remnant, which emits in the MHz frequency range, is expected to form as the ejected bubbles coalesce outside the system. Furthermore, the KH instability triggers turbulence in the outflow, which eventually heats the gas and results in optical flares outside the white dwarf ’s Roche lobe. On its trajectory outwards, the outflow disrupts the magnetic field of the secondary and currents are induced that may heat plasma trapped in the field to X-ray emitting temperatures. This Joule heated plasma can account for the observed non-pulsed X-ray emission from AE Aqr.