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Astron. Astrophys. 334, 742-745 (1998)

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Ambipolar diffusion in star-forming clouds

A. Hujeirat

Astronomisches Institut der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany (hujeirat@astro.uni-wuerzburg.de)

Received 2 September 1997 / Accepted 5 March 1998


The dynamical collapse of a magnetically supported molecular cloud with ambipolar diffusion (hereafter AD) is numerically investigated.

Each of the five cloud models considered here has a fixed mass of 1 [FORMULA], a prescribed outer boundary where the normal derivative of the total pressure vanishes. In these models, there is no dynamical collapse if AD is excluded.

It is shown that owing to the strong non-linearity exhibiting the effective AD term, AD appears to be operating in different regions with completely different time scales. The models with AD undergo dynamical contraction on a dilute free-fall time scale ([FORMULA]) ranging between [FORMULA] depending on the ionization fraction in the cloud considered.

It is shown that a shock is always formed at the center which thereafter propagates radially outwards into the high latitudinal regions leaving quasi magnetohydrostatic density profiles behind its shock front. If AD is present, these structures do not survive and start to collapse to form a central point mass surrounded by a highly condensed disk-like configuration. Thus, AD is actually able to change the flow configuration on time scales comparable to fractions of [FORMULA].

Furthermore, AD appears to give rise to an inside-outside collapse via a magnetosonic expansion wave which starts its motion from the center.

Key words: stars: formation – ISM: clouds – ISM: magnetic fields – MHD

Send offprint requests to: A. Hujeirat

© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998