Force-free and Potential Models of a Filament Channel in Which a Filament Forms

Few examples of the creation of a filament channel or filament have ever been documented. In a recent paper, Gaizauskas and coworkers observed the early stages of creation of such a channel and then the formation of a filament in it. The filament channel was born when a new activity complex emerged near an old, decaying bipolar active region. The filament itself then formed after convergence of flux in the channel.

In this paper, force-free models are constructed for two phases of the channel's development. For the early days, the models show that the formation of the filament channel seen in Hα is due to the emerging activity complex. The field lines that give the best comparison to the fibril observations are low-lying and have a strong horizontal component. Later, when the activity complex has matured and a filament has formed between it and the adjacent decaying bipolar region, the models give a good representation of the path of the filament in the channel. It is found that the presence of flat or dipped field lines and of converging flux are necessary but not sufficient conditions for filament formation. Furthermore, the magnetic field lines of the filament itself form a narrow, vertical, sheetlike flux-tube corridor that is flat and low-lying. It connects one particular magnetic source to a sink and is bounded by separatrix surfaces that separate the filament from the old remnant region and most of the newly emerged flux.