The bunching of giant planets at a distance of several stellar radii may be
explained by the disruption of the inner part of the disk by the magnetosphere
of the star during the T Tauri stage of evolution. The rotating magnetic field
of the star gives rise to a low density magnetospheric gap where stellar
migration is strongly suppressed. We performed full 3D magnetohydrodynamic
simulations of the disk-magnetosphere interaction and examined conditions for
which the magnetospheric gap is "empty", by changing the misalignment angle
between magnetic and rotational axes of the star, Theta, and by lowering the
adiabatic index gamma, which mocks up the effect of heat conductivity and
cooling. Our simulations show that for a wide range of plausible conditions the
gap is essentially empty. However, in the case of large misalignment angles
Theta, part of the funnel stream is located in the equatorial plane and the gap
is not empty. Furthermore, if the adiabatic index is small (gamma=1.1) and the
rotational and magnetic axes are almost aligned, then matter penetrates through
the magnetosphere due to 3D instabilities forming high-density equatorial
funnels. For these two limits there is appreciable matter density in the
equatorial plane of the disk so that a planet may migrate into the star.Comment: 6 pages, 6 figures, Accepted to the ApJ Letters. See version of the
paper with higher resolution plots at
http://astrosun2.astro.cornell.edu/us-rus/planets.ht