Summary and problems ahead

We have illustrated a model which attempts to link the stability of the magnetosphere with the disc resistivity, which sets an electromagnetic boundary condition for the magnetosphere. The nature of the disc-star interaction would imply that the magnetospheric effect on the disc will in general react back on the disc. Since the constant accretion rate is assumed, the disc viscosity and resistivity become functions of the total angular momentum flux or the change of the spin rate. As argued, such a mutual interaction leads to a magnetospheric instability which enables the outer magnetosphere alternating between two states.

The full awareness of the underlying physics associated with Cen X-3 clearly needs further work beyond a semi-quantitative level, as the physical process involved would be more complicated than what outlined. Among several approximations, the most uncertain aspects are probably (1) the quasi-steady state approach for the angular momentum flux and (2) the unchanged accretion rate. Detailed work must include the density variation and adopt time-dependent analysis. Nevertheless, given the exploratory nature of our work to a highly complicated system, our investigation has so far yielded valuable insight upon which further studies are based.

© Copyright Astronomical Society of Australia 1997