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Comment: 19 pages, LaTeX, 9 Postscript figures. Astronomy and Astrophysics, in press
Comment: 22 pages, 10 figures, LaTeX. Earth and Planetary Sciences, in press
Comment: 6 pages (LaTeX), no Figures to be published in The Astrophysical Journal Letters
Comment: 10 pages (LaTeX), 7 Figures to be published in Monthly Notices of the Royal Astronomical Society
Statistical analysis of space navigation systems based on multivariate Gaussian distributions and linear perturbation theory
[[abstract]]In this paper we follow the evolution of an unstable magnetized cloud core modeled with the density distribution of a singular isothermal sphere and threaded by a uniform magnetic field. We include neutral-ion slip, and we solve the equations by an expansion about the known self-similar problem without magnetism. We find that the magnetic field does not significantly modify the standard rate of mass infall because of two offsetting effects: the Lorentz force that impedes gravitational collapse, and the increased characteristic speed that causes the initiation of infall to travel outward faster (as a fast magnetohydrodynamic wave rather than an acoustic wave). Strong magnetic pinching forces deflect infalling gas toward the equatorial plane to form a flattened disequilibrium structure (''pseudodisk'') around the central prot...
[[abstract]]In a previous paper (Paper I) we presented a perturbative analysis of the collapse of a molecular cloud-core threaded by an ordered magnetic field, obtaining a semianalytical solution applicable over a moderate range of temporal and spatial scales. In the present paper we supplement this analysis with a numerical solution of the magnetohydrodynamic (MHD) equations that include the effects of ambipolar diffusion, valid in the region where magnetic effects dominate the dynamics of the collapse. We focus on the formation of a flattened disequilibrium structure (''pseudodisk'') around the central protostar. The numerical solution gives dimensionless values for the radius of the pseudodisk as a function of time. Combined with the analytical scaling laws found in Paper I, these results provide in the small time limit a simple pow...
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