THE ACCRETION OF DIAMAGNETIC BLOBS BY A ROTATING MAGNETOSPHERE

In some close binary systems the accretion flow may consist largely of gas blobs which are not threaded by the magnetic field of the accretor, but interact with it through a surface drag. I show analytically that blobs of initial specific energy and angular momentum E < 0, J are accreted if and only if 2 (-E)/J exceeds a quantity close to the spin rate omega of the star. For Roche lobe overflow, this naturally gives the relation (equilibrium spin period) approximately 0.1 x (orbital period), satisfied by some intermediate polars. The magnetic field circularizes the blob orbits without the intervention of viscosity or the formation of an extended accretion disc.