Miljenko Čemeljić, Hsien Shang, Tzu-Yang Chiang
We investigate the launching of outflows in the close vicinity of a young
stellar object, treating the innermost portion of an accretion disk as a
gravitationally bound reservoir of matter. By solving the resistive MHD
equations with our version of the Zeus-3D code with implemented resistivity, we
study the effect of magnetic diffusivity in the magnetospheric
accretion-ejection mechanism. Physical resistivity has been included in the
whole computational region. We show, for the first time, that quasi-stationary
outflows consisting of axial and conical components can be launched from a
purely resistive magnetosphere. We identify four stages of magnetospheric
interaction with distinctly different geometries of the magnetic field, and
describe the effect of magnetic reconnection in re-shaping the magnetic field.
The stages are the relaxation, reconnection and infall, after which two outflow
components can be seen in a final flow: a fast axial component launched from
above the star, dominated by magnetic pressure, and a slow conical component,
launched from the opened resistive magnetosphere of a disk gap, between the
star and the disk inner radius. We show how outflows depend on the disk to
corona density ratio and on strength of the magnetic field, and compare the
position of the disk truncation radius with theoretical predictions. Results
from previous investigations with resistive MHD in the literature, which have
been obtained with various setups, are recovered in our simulations.
Comparisons are thus made easier for more general purposes, by identifying
previous features in the simulations within the different stages of our
simulation.
View original:
http://arxiv.org/abs/1112.6226
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