Model prediction for an observed filament

This paper presents the results of a "blind test" for modeling the structur e of an observed filament using the three-dimensional magnetohydrostatic mo del recently developed by Aulanier et al. in 1999. The model uses a constan t shear a, and it takes into account the effects of pressure and gravity. T he test consisted of predicting the structure of a filament (observed in th e southern hemisphere) with a minimum observational input: only a line-of-s ight magnetogram, with a straight line drawn on it to show the location of the filament, was provided. The filament was chosen by the observers (N. S. and S. F. M.) because it had a definite overall left-handed structural pat tern known as sinistral but the direction of component of the magnetic held along the filament axis was uncertain from the combination of Ha data and magnetograms. The modeler (G. A.) evaluated and fixed the values of some of the free parameters of the model while some others were varied in reasonab le ranges. The Ha image of the filament was revealed only after the modelin g. For alpha > 0, the three-dimensional distribution of magnetic dips compu ted by the model fairly well reproduces the structure of the filament and i ts barbs. Moreover, the models for which alpha < 0 do not match well the ob servations. This study then shows the first successful theoretical predicti on for the magnetic held of an observed filament. It shows that the method based on the Aulanier et al. model is a powerful tool, not only for purpose s of modeling, but also for prediction of the chirality, helicity, and morp hology of observed filaments.