Effect of Dust Evaporation on the Fossil Magnetic Field of Young Stars and Their Accretion Disks

The theory of the fossil magnetic field of young stars and their accretion disks has been verified by comparing the observational data with the results of numerical simulations of the collapse of protostellar clouds. A new model of dust evaporation has been proposed, in which the parameter is not the thickness of the mantles, but the initial ratio of the core radius to the mantle radius of a dust grain. A semi-analytical description of the evolution of the radius distribution of dust grains was constructed. On its basis, the variations in the relative number density of dust grains, as well as the average values of the radius, cross-sectional area, and mass of dust grains, were calculated. It was shown that at the stage of disappearance of dust cores, these averages reach their maxima, but this does not affect the interaction of dust with gas particles, since the dust becomes scarce. Using cloud models W3 (main), NGC 2024, and DR 21 OH1, it has been demonstrated that neglecting dust evaporation underestimates the fossil magnetic field by several times. The possibility of formation of a magnetic compaction at the outer boundary of the zone of strong magnetic field diffusion (dead zone) has been confirmed. It is concluded that a correct calculation of dust evolution, ionization of the medium, and collapse anisotropy makes it possible to match the theoretical and observed magnetic fields of young stars and their accretion disks.