EDP Sciences
Free access
Volume 395, Number 3, December I 2002
Page(s) 1045 - 1060
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20021442

A&A 395, 1045-1060 (2002)
DOI: 10.1051/0004-6361:20021442

Formation of protostellar jets - effects of magnetic diffusion

C. Fendt1, 2 and M. Cemeljic2

1  Universität Potsdam, Institut für Physik, Am Neuen Palais 10, 14469 Potsdam, Germany
2  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
    e-mail: cfendt@aip.de;cemeljic@aip.de

(Received 24 May 2002 / Accepted 24 September 2002 )

Protostellar jets most probably originate in turbulent accretion disks surrounding young stellar objects. We investigate the evolution of a disk wind into a collimated jet under the influence of magnetic diffusivity, assuming that the turbulent pattern in the disk will also enter the disk corona and the jet. Using the ZEUS-3D code in the axisymmetry option we solve the time-dependent resistive MHD equations for a model setup of a central star surrounded by an accretion disk. The disk is taken as a time-independent boundary condition for the mass flow rate and the magnetic flux distribution. We derive analytical estimates for the magnitude of magnetic diffusion in a protostellar jet connecting our results to earlier work in the limit of ideal MHD. We find that the diffusive jets propagate slower into the ambient medium, most probably due to the lower mass flow rate in the axial direction. Close to the star we find that a quasi stationary state evolves after several hundred (weak diffusion) or thousand (strong diffusion) disk rotations. Magnetic diffusivity affects the protostellar jet structure as follows. The jet poloidal magnetic field becomes de-collimated. The jet velocity increases with increasing diffusivity, while the degree of collimation for the hydrodynamic flow remains more or less the same. We suggest that the mass flux is a proper tracer for the degree of jet collimation and find indications of a critical value for the magnetic diffusivity above which the jet collimation is only weak. We finally develop a self-consistent picture in which all these effects can be explained in the framework of the Lorentz force.

Key words: accretion, accretion disks -- MHD -- ISM: jets and outflows -- stars: mass loss -- stars: pre-main sequence -- galaxies: jets

Offprint request: C. Fendt, cfendt@aip.de

© ESO 2002

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.