Issue A&A Volume 460, Number 1, December II 2006 Page(s) 1 - 14 Section Astrophysical processes DOI http://dx.doi.org/10.1051/0004-6361:20065484

A&A 460, 1-14 (2006)
DOI: 10.1051/0004-6361:20065484

Two-component magnetohydrodynamical outflows around young stellar objects

Interplay between stellar magnetospheric winds and disc-driven jets

Z. Meliani^{1, 2, 3}, F. Casse², and C. Sauty<sup>1

1</sup>  Observatoire de Paris, L.U.Th., 92190 Meudon, France
    e-mail: [zakaria.meliani;Christophe.Sauty]@obspm.fr
²  AstroParticule & Cosmologie (APC), Université Paris 7, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France
    e-mail: fcasse@apc.univ-paris7.fr
³  Max Planck Institute for Astrophysics, Box 1317, 85741 Garching, Germany

(Received 24 April 2006 / Accepted 4 August 2006)

Abstract
Context.We present the first-ever simulations of non-ideal magnetohydrodynamical (MHD) stellar magnetospheric winds coupled with disc-driven jets where the resistive and viscous accretion disc is self-consistently described.
Aims. These innovative MHD simulations are devoted to the study of the interplay between a stellar wind (having different ejection mass rates) and an MHD disc-driven jet embedding the stellar wind.
Methods.The transmagnetosonic, collimated MHD outflows are investigated numerically using the VAC code. We first investigate the various angular momentum transports occurring in the magneto-viscous accretion disc. We then analyze the modifications induced by the interaction between the two components of the outflow.
Results.Our simulations show that the inner outflow is accelerated from the central object's hot corona thanks to both the thermal pressure and the Lorentz force. In our framework, the thermal acceleration is sustained by the heating produced by the dissipated magnetic energy due to the turbulence. Conversely, the outflow launched from the resistive accretion disc is mainly accelerated by the magneto-centrifugal force.
Conclusions.The simulations show that the MHD disc-driven outflow extracts angular momentum more efficiently than do viscous effects in near-equipartition, thin-magnetized discs where turbulence is fully developed. We also show that, when a dense inner stellar wind occurs, the resulting disc-driven jet has a different structure, namely a magnetic structure where poloidal magnetic field lines are more inclined because of the pressure caused by the stellar wind. This modification leads to both an enhanced mass-ejection rate in the disc-driven jet and a larger radial extension that is in better agreement with the observations, besides being more consistent.

Key words: stars: winds, outflows -- magnetohydrodynamics (MHD) -- accretion, accretion disks -- acceleration of particles -- stars: mass-loss -- stars: pre-main sequence

© ESO 2006

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