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Astron. Astrophys. 354, 1041-1052 (2000)


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Protostellar masses versus ionization fraction in star-forming clouds

A. Hujeirat 1, M. Camenzind 1 and H.W. Yorke 2

1 Landessternwarte-Koenigstuhl, 69117 Heidelberg, Germany
2 Jet Propulsion Laboratory, California Institute of Technology, MS 169-506, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Received 31 May 1999 / Accepted 20 January 2000

Abstract

We study the dynamical evolution of self-gravitating magnetic cloud cores with an implicit MHD code for different dependencies of the ionization fraction on density. Assuming magnetically subcritical cloud cores initially similar in every respect except for the degree of ionization, we show that moderately and highly ionized cores tend to form more massive objects than their weakly ionized counterparts. Including the effects of rotation and/or more efficient cooling enhances this difference. Whereas the collapse of a weakly ionized core occurs on the free-fall time scale and independent of the boundary conditions, the onset of collapse in moderately or highly ionized media depends strongly on the flow of material along magnetic field lines through the boundaries.

We discuss the possibility that fast, large scale gravitationally induced inflows are likely to occur along the lines of strong magnetic fields threading a highly ionized self-gravitating core. Based on our numerical results, we conclude that the ratio of mass to magnetic flux should be considered in combination with ionization fraction in order to estimate the mass of the object which can be expected to result from non-isolated core collapse.

Key words: magnetic fields – Magnetohydrodynamics (MHD) – stars: formation – ISM: clouds – ISM: magnetic fields

Send offprint requests to: A. Hujeirat

© European Southern Observatory (ESO) 2000

Online publication: February 25, 2000

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