  We studied the collapse of rotating molecular cloud cores with inclined
magnetic fields, based on three-dimensional numerical simulations.The numerical
simulations start from a rotating Bonnor-Ebert isothermal cloud in a uniform
magnetic field. The magnetic field is initially taken to be inclined from the
rotation axis. As the cloud collapses, the magnetic field and rotation axis
change their directions. When the rotation is slow and the magnetic field is
relatively strong, the direction of the rotation axis changes to align with the
magnetic field, as shown earlier by Matsumoto & Tomisaka. When the magnetic
field is weak and the rotation is relatively fast, the magnetic field inclines
to become perpendicular to the rotation axis. In other words, the evolution of
the magnetic field and rotation axis depends on the relative strength of the
rotation and magnetic field. Magnetic braking acts to align the rotation axis
and magnetic field, while the rotation causes the magnetic field to incline
through dynamo action. The latter effect dominates the former when the ratio of
the angular velocity to the magnetic field is larger than a critical value
\Omega_0/ B_0 > 0.39 G^1/2 c_s^-1, where B_0, \Omega_0, G, and c_s^-1 denote
the initial magnetic field, initial angular velocity, gravitational constant,
and sound speed, respectively. When the rotation is relatively strong, the
collapsing cloud forms a disk perpendicular to the rotation axis and the
magnetic field becomes nearly parallel to the disk surface in the high density
region. A spiral structure appears due to the rotation and the wound-up
magnetic field in the disk.
