We examine the morphology of magnetic structures in thin plasma accretion disks, generalizing a stationary ideal magnetohydrodynamics model for the time-dependent viscoresistive case. Our analysis deals with small-scale perturbations to a central dipolelike magnetic field, which give rise - as in the ideal case - to the periodic modulation of magnetic flux surfaces along the radial direction, corresponding to the formation of a toroidal current channel's sequence. These microstructures suffer an exponential damping in time because of the nonzero resistivity coefficient, allowing us to define a configuration lifetime which mainly depends on the midplane temperature and on the length scale of the structure itself. By means of this lifetime, we show that the microstructures can exist within the inner regions of stellar disks in a defined range of temperatures, precisely for radii of Râ‰2109cm and temperatures of 104Kâ‰2T≠2105K. Their duration - minutes to hours - is shown to be consistent with local transient phenomena rather than with a steady equilibrium. © 2013 American Physical Society.

Nonstationary magnetic microstructures in stellar thin accretion disks

Montani, G.
2013

Abstract

We examine the morphology of magnetic structures in thin plasma accretion disks, generalizing a stationary ideal magnetohydrodynamics model for the time-dependent viscoresistive case. Our analysis deals with small-scale perturbations to a central dipolelike magnetic field, which give rise - as in the ideal case - to the periodic modulation of magnetic flux surfaces along the radial direction, corresponding to the formation of a toroidal current channel's sequence. These microstructures suffer an exponential damping in time because of the nonzero resistivity coefficient, allowing us to define a configuration lifetime which mainly depends on the midplane temperature and on the length scale of the structure itself. By means of this lifetime, we show that the microstructures can exist within the inner regions of stellar disks in a defined range of temperatures, precisely for radii of Râ‰2109cm and temperatures of 104Kâ‰2T≠2105K. Their duration - minutes to hours - is shown to be consistent with local transient phenomena rather than with a steady equilibrium. © 2013 American Physical Society.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.12079/667
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