Model Prediction for an Observed Filament

This paper presents the results of a ``blind test'' for modeling the structure of an observed filament using the three-dimensional magnetohydrostatic model recently developed by Aulanier et al. in 1999. The model uses a constant shear α, and it takes into account the effects of pressure and gravity. The test consisted of predicting the structure of a filament (observed in the southern hemisphere) with a minimum observational input: only a line-of-sight 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 pattern known as sinistral, but the direction of component of the magnetic field along the filament axis was uncertain from the combination of Hα 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 reasonable ranges. The Hα image of the filament was revealed only after the modeling. For α>0, the three-dimensional distribution of magnetic dips computed by the model fairly well reproduces the structure of the filament and its barbs. Moreover, the models for which α<0 do not match well the observations. This study then shows the first successful theoretical prediction for the magnetic field of an observed filament. It shows that the method based on the Aulanier et al. model is a powerful tool, not only for purposes of modeling, but also for prediction of the chirality, helicity, and morphology of observed filaments.