Angular Momentum Evolution from Core to Disk Scales in the Early Phase of Star Formation: Constraints from HH 212, HH 211, and B335
I investigate the angular momentum evolution from core to disk scales in the early phase of star formation using three protostellar systems: HH 212, HH 211, and B335. Observations show that the specific angular momentum follows a power-law dependence at core scales and transitions to an approximately constant value at smaller radii, indicating dynamical collapse in the inner envelope. I model this behavior using the inside-out collapse solution of Shu (1977) and its rotating extension, the Terebey-Shu-Cassen model, including modest magnetic effects through a flattened, magnetized core. I find that the observed angular momentum profiles in all three sources are broadly consistent with an inside-out collapse scenario with approximate conservation of specific angular momentum in the collapsing region. The inferred collapse ages and mass infall rates yield total masses accreted onto the center that are broadly consistent with the central masses derived from kinematics, allowing for a fraction of the material to be ejected by jets and winds. The predicted midplane densities at typical radii, including the effect of magnetic flattening, are also consistent with observational estimates. The three systems exhibit a similar pattern of angular momentum evolution despite large differences in the magnitude of their specific angular momentum. In particular, the small disk in B335 can be naturally explained by its lower initial specific angular momentum, although alternative explanations, such as magnetic braking or different initial conditions, cannot be excluded. These results suggest that inside-out collapse, with modest magnetic modification, provides a plausible first-order description of angular momentum evolution from core to disk scales in the early phase of star formation.