Abstract

Solar filaments and prominences have been observed for more than one and a half century. However, the detailed nature of their magnetic structure and dynamics remain poorly understood. Here we analyze a cusp-shaped polar-crown prominence observed by the SDO /AIA imager and H alpha MSDP spectrograph (Bialkow). The prominence consists of two parts, one of which show a large bubble underneath. Analysis of the AIA intensity profiles show that the bubble-related emission is equivalent or less than the coronal intensity at the same altitude. The observed prominence is modeled by a linear force-free model containing a flux rope perturbed by inclusion of parasitic bipoles. Sheared bipoles lead to formation of cusp-shaped prominences with bubbles similar to the observed ones. Projection eects create illusion of vertical structures. While the prominence body contains magnetic dips, the magnetic field geometry in the bubble is that of an arcade. These different flux systems are separated by fan surfaces of two magnetic null-points. The fan surfaces intersect at a separator located at the boundary between the bubble and the prominence body. We conjecture that the formation of plumes involves reconnection at the separator.