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 ev er been documented. In a recent paper, Gaizauskas and coworkers observ ed the early stages of creation of such a channel and then the formati on of a filament in it. The filament channel was born when a new activ ity complex emerged near an old, decaying bipolar active region. The f ilament itself then formed after convergence of flux in the channel. I n this paper, force-free models are constructed for two phases of the channel's development. For the early days, the models show that the fo rmation of the filament channel seen in Ha is due to the emerging acti vity complex. The field lines that give the best comparison to the fib ril observations are low-lying and have a strong horizontal component. Later, when the activity complex has matured and a filament has forme d 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 conver ging flux are necessary but not sufficient conditions for filament for mation. Furthermore, the magnetic field lines of the filament itself f orm a narrow, vertical, sheetlike flux-tube corridor that is hat and l ow-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.