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Astron. Astrophys. 335, 309-322 (1998)


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3-D magnetic configurations supporting prominences

II. The lateral feet as a perturbation of a twisted flux-tube

G. Aulanier 1, P. Démoulin 1, L. van Driel-Gesztelyi 1, 2, P. Mein 1 and C. DeForest 3

1 Observatoire de Paris, Section Meudon, DASOP, URA 2080 (CNRS), F-92195 Meudon Principal Cedex, France
2 Konkoly Observatory, Pf., H-1525 Budapest, Hungary
3 NASA/Goddard SFC, Greenbelt, MD 20771, USA

Received 21 October 1997 / Accepted 9 March 1998

Abstract

In a previous paper we have shown that a twisted flux-tube is the most probable magnetic configuration supporting prominences. The model interprets many observations in a natural way (in particular the magnetic measurements in prominences and the chirality properties). Moreover, prominence feet appear as a direct consequence of the parasitic polarities present in the filament channel. Here we investigate further the link between feet and parasitic polarities by modelling explicitly these polarities. We show that the prominence lateral feet appear naturally, above secondary photospheric inversion lines and we describe the morphological change of feet as parasitic polarities evolve. This approach is applied to an observed filament in [FORMULA] with the MSDP on the German VTT (Tenerife) where SOHO/MDI magnetograms are available. We show that the shape of the prominence is defined by the distribution of the dips in the computed magnetic configuration. Then we analyse the topology of the magnetic field using the quasi-separatrix layers (QSLs) method. We describe the basic changes in the topology as the parasitic polarities evolve, in particular how the configuration pass from an OX to an OF topology. We find a correspondance between the computed QSLs and some of the chromospheric brightenings, observed around the feet of filaments in the y line (Ca II, 8542 Å). It confirms the deduced magnetic configuration and shows that energy release is present at a low level in the complex topology of the filament configuration.

Key words: magnetic fields – Sun: chromosphere – Sun: magnetic fields – Sun: prominences – Sun: filaments

Send offprint requests to: G. Aulanier

© European Southern Observatory (ESO) 1998

Online publication: June 12, 1998

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