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G. Aulanier (NRL), P. Demoulin (DASOP, Observatoire de Meudon)
Despite of the large number of 2D and 3D models for the magnetic fields in prominences, none has been succesfully directly compared with observational data untill recently, even if many of them still satisfied some well established observational results. This has led to a never ending controversy between theorists and observers, about the relevance of dipped field lines for mass support against gravity in these objects.
Here we present a new 3D magnetohydrostatic model based on dipped field lines. The main body of the filament is formed by a twisted flux rope in a bipolar region, and we show how small parasitic polarities near the neutral line lead to a local perturbation of the magnetic fields in the corona, leading to the formation of lateral dips, which appear aside from the flux rope. We show that these are formed by local expansions of the fluxe rope, as well as by the bending of some surrounding sheared field lines, toward the photospheric parasitic polarities. We suggest that these lateral dips can form lateral feet of filaments. Moreover the global magnetic configuration shows in a natural fashion a very large number of typical observational aspects of prominences.
Using a magnetogram obtained by SOHO/MDI on 09/25/96 as boundary conditions, we extrapolate the magnetic field under the assumptions of the model. Comparing the 3D distribution of dips with the morphology of the filament observed in H\alpha on the German VTT (Tenerife) at the same time, we show a good correlation between the dips and the filament body, as well as with its lateral feet.
All these results suggest that the model is well adapted for the description of the magnetic field in filaments and their close environement. Furthermore its direct comparison with observations provide evidence in favor of dipped field lines in prominences.
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