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D.A. Uzdensky (Univ. of Chicago)
We examine the behavior of the magnetic field lines in a magnetically linked star--disk system. The rotation of the accretion disk with respect to the central star causes the field lines to twist up and inflate dramatically on the rotation period time scale. Our main goal is to see under which conditions the expanding field lines could form a thin current sheet in the magnetosphere above the disk, as the twist angle is increased. In order to investigate this question, we develop a simple analytical model based on the force-free Grad-Shafranov equation. This model enables us to estimate the angular width of the current concentration region in terms of the twist angle of the field lines. We observe that thin structures in the magnetosphere may form in the case of a nonuniformly rotating disk, in particular, for field lines attached to the disk in the region where the twist angle varies rapidly with radius (e.g., at the inner edge of the disk). We discuss the relevance of our findings to the possibility of magnetic reconnection above the disk, as well as some other astrophysical implications.
Work supported by ASCII/Alliances Center for Astrophysical Thermonuclear Flashes under DOE subcontract B341495.
The author(s) of this abstract have provided an email address for comments about the abstract: uzdensky@oddjob.uchicago.edu