We use magnetic collapse models to place some constraints on the formationand angular momentum evolution of circumstellar disks which are embedded inmagnetized cloud cores. Previous models have shown that the early evolution ofa magnetized cloud core is governed by ambipolar diffusion and magneticbraking, and that the core takes the form of a nonequilibrium flattenedenvelope which ultimately collapses dynamically to form a protostar. In thispaper, we focus on the inner centrifugally-supported disk, which is formed onlyafter a central protostar exists, and grows by dynamical accretion from theflattened envelope. We estimate a centrifugal radius for the collapse of massshells within a rotating, magnetized cloud core. The centrifugal radius of theinner disk is related to its mass through the two important parameterscharacterizing the background medium: the background rotation rate $\Omb$ andthe background magnetic field strength $\Bref$. We also revisit the issue ofhow rapidly mass is deposited onto the disk (the mass accretion rate) and useseveral recent models to comment upon the likely outcome in magnetized cores.Our model predicts that a significant centrifugal disk (much larger than astellar radius) will be present in the very early (Class 0) stage ofprotostellar evolution. Additionally, we derive an upper limit for the diskradius as it evolves due to internal torques, under the assumption that thestar-disk system conserves its mass and angular momentum even while most of themass is transferred to a central star.
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