Structuring and support by Alfvén waves around prestellar cores

Free access article

Issue		A&A Volume 414, Number 2, February I 2004


Page(s)		559 - 572
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20031647

A&A 414, 559-572 (2004)
DOI: 10.1051/0004-6361:20031647

Structuring and support by Alfvén waves around prestellar cores

D. Folini¹, J. Heyvaerts¹ and R. Walder²

¹ Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
² Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA

(Received 22 August 2002 / Accepted 1 October 2003 )

Abstract
Observations of molecular clouds show the existence of starless, dense cores, threaded by magnetic fields. Observed line widths indicate these dense condensates to be embedded in a supersonically turbulent environment. Under these conditions, the generation of magnetic waves is inevitable. In this paper, we study the structure and support of a 1D plane-parallel, self-gravitating slab, as a monochromatic, circularly polarized Alfvén wave is injected in its central plane. Dimensional analysis shows that the solution must depend on three dimensionless parameters. To study the nonlinear, turbulent evolution of such a slab, we use 1D high resolution numerical simulations. For a parameter range inspired by molecular cloud observations, we find the following. 1) A single source of energy injection is sufficient to force persistent supersonic turbulence over several hydrostatic scale heights. 2) The time averaged spatial extension of the slab is comparable to the extension of the stationary, analytical WKB solution. Deviations, as well as the density substructure of the slab, depend on the wave-length of the injected wave. 3) Energy losses are dominated by loss of Poynting-flux and increase with increasing plasma beta. 4) Good spatial resolution is mandatory, making similar simulations in 3D currently prohibitively expensive.

Key words: turbulence -- magnetohydrodynamics (MHD) -- ISM: clouds -- ISM: kinematics and dynamics -- ISM: magnetic fields -- ISM: structure

Offprint request: D. Folini, folini@astro.u-strasbg.fr

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