  We investigate whether magnetic tension can define the masses of forming
stars by holding up the subcritical envelope of a molecular cloud that suffers
gravitational collapse of its supercritical core. We perform an equilibrium
analysis of the initial and final states assuming perfect field freezing, no
rotation, isothermality, and a completely flattened configuration. The sheet
geometry allows us to separate the magnetic tension into a levitation
associated with the split monopole formed by the trapped flux of the central
star and a suspension associated with curved field lines that thread the static
pseudodisk and envelope of material external to the star. We find solutions
where the eigenvalue for the stellar mass is a fixed multiple of the initial
core mass of the cloud. We verify the analytically derived result by an
explicit numerical simulation of a closely related 3-D axisymmetric system.
However, with field freezing, the implied surface magnetic fields much exceed
measured values for young stars. If the pinch by the central split monopole
were to be eliminated by magnetic reconnection, then magnetic suspension alone
cannot keep the subcritical envelope (i.e., the entire model cloud) from
falling onto the star. We argue that this answer has general validity, even if
the initial state lacked any kind of symmetry, possessed rotation, and had a
substantial level of turbulence. These findings strongly support a picture for
the halt of infall that invokes dynamic levitation by YSO winds and jets, but
the breakdown of ideal magnetohydrodynamics is required to allow the appearance
in the problem of a rapidly rotating, centrifugally supported disk. We use
these results to calculate the initial mass function and star formation
efficiency for the distributed and clustered modes of star formation.
