title: Nonstationary magnetic microstructures in stellar thin accretion disks.
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 R</~10(9)cm and temperatures of 10(4)K</~T</~10(5)K. Their duration-minutes to hours-is shown to be consistent with local transient phenomena rather than with a steady equilibrium.
authors.affiliation: ENEA-Centro Ricerche Frascati, U.T. Fus. (FUSMAG Laboratory), Via Enrico Fermi 45, 00044 Frascati, Rome, Italy. giovanni.montani@frascati.enea.it
authors.forename: Giovanni
authors.initials: G
authors.lastname: Montani
authors.forename: Jacopo
authors.initials: J
authors.lastname: Petitta
mesh_terms: D003198:Computer Simulation; D017097:Electric Impedance; D060526:Magnetic Fields; D008956:Models, Chemical; D008958:Models, Molecular; D058626:Plasma Gases / Q000737:chemistry*; D013696:Temperature; D014783:Viscosity
chemical_list: D058626:Plasma Gases