We discuss three specific modes of accretion disks around rotating magnetized
neutron stars which may explain the separations of the kilo Hertz quasi
periodic oscillations (QPO) seen in low mass X-ray binaries. The existence of
these modes requires that there be a maximum in the angular velocity of the
accreting material, and that the fluid is in stable, nearly circular motion
near this maximum rather than moving rapidly towards the star or out of the
disk plane into funnel flows. It is presently not known if these conditions
occur, but we are exploring this with 3D magnetohydrodynamic simulations and
will report the results elsewhere. The first mode is a corotation mode which is
radially trapped in the vicinity of the maximum of the disk rotation rate and
is unstable. The second mode, relevant to relatively slowly rotating stars, is
a magnetically driven eccentric (m=1) oscillation of the disk excited at a
Lindblad radius in the vicinity of the maximum of the disk rotation. The third
mode, relevant to rapidly rotating stars, is a magnetically coupled eccentric
(m=1) and an axisymmetric (m=0) radial disk perturbation which has an inner
Lindblad radius also in the vicinity of the maximum of the disk rotation. We
suggest that the first mode is associated with the upper QPO frequency,
Ξ½uβ, the second with the lower QPO frequency, Ξ½ββ=Ξ½uββΞ½ββ, and
the third with the lower QPO frequency, Ξ½ββ=Ξ½uββΞ½ββ/2, where Ξ½ββ
is the star's rotation rate.Comment: 6 pages, 2 figure