Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...308.1013s&link_type=abstract
Astronomy and Astrophysics, v.308, p.1013-1032
Astronomy and Astrophysics
Astrophysics
4
Accretion, Accretion Disks, Magnetohydrodynamics, Plasmas, Numerical Methods
Scientific paper
The dynamics of a single slender, magnetized torus in an isothermal standard thin accretion disk is considered. The torus is assumed to have small dimensions compared to the distance to the central object so that a local approximation can be adopted. The dynamics of a slender torus are essentially determined by the so-called shear parameter S which is a measure of the relative importance of tube stretching by inertial forces and the effects of magnetic tension which tends to decrease the length of a curved flux tube. For relatively weak magnetic fields, the strong shear limit S>>1, sections of the tube are dragged along passively by the surrounding flow, leading to a large increase of the tube length and, consequently, to a considerable enhancement of the magnetic field strength. Moreover, the rate of stretching varies throughout the tube and this gives rise to the formation of two vertical loop-like structures which may be considered as the progenitors of coronal loops. For relatively strong magnetic fields (S<<1, weak shear limit), the tube major radius collapses until a quasi-stationary equilibrium is reached. In this state, the density variation along the tube is negligible so that no vertical loops are formed. The tube is dense so that it rises out of the disk slowly. A tube having intermediate values of S shows a more complex behaviour which has features of both extremes. It is argued that these results hold qualitatively under more general disk stratification laws.
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