Disk accretion onto a magnetized star
  The problem of interaction of the rotating magnetic field, frozen to a star,
with a thin well conducting accretion disk is solved exactly. It is shown that
a disk pushes the magnetic field lines towards a star, compressing the stellar
dipole magnetic field. At the point of corotation, where the Keplerian rotation
frequency coincides with the frequency of the stellar rotation, the loop of the
electric current appears. The electric currents flow in the magnetosphere only
along two particular magnetic surfaces, which connect the corotation region and
the inner edge of a disk with the stellar surface. It is shown that the closed
current surface encloses the magnetosphere. Rotation of a disk is stopped at
some distance from the stellar surface, which is 0.55 of the corotation radius.
Accretion from a disk spins up the stellar rotation. The angular momentum
transferred to the star is determined.
