Flare loop geometry |
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| Authors: | Nitta N Van Driel-Gesztelyi L Harra-Murnion LK |
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| Institution: | (1) Lockheed Martin Solar and Astrophysics Laboratory, O/L9-41, B/252, 3251 Hanover Street, USA;(2) Section de Meudon, DASOP, Observatoire de Paris, F-92125 Meudon, Principal Cedex, France;(3) Konkoly Observatory, Budapest, Pf. 67, H-1525, Hungary;(4) Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surry, RH5 6NT, U.K |
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| Abstract: | In selected flares that occurred in AR 7260, we have studied the geometry of the brightest soft X-ray loop by tracing it on an image. Even under the assumption that the loop is contained in a plane, it is clear that a single image does not permit us to determine the full geometry. It only provides possible loop shapes as a function of the inclination angle of the loop plane with respect to the vertical. However, all the loops that reproduce the observed appearance give the same direction of increasing height as projected on to the image plane. This direction is compared with two relevant observations. Based on 2-D reconnection models that involve a cusp configuration, it is expected that the soft X-ray loop top source moves upward with time and that a higher temperature region exists above the loop top. Several flares are found to contradict these predictions, presumably implying the inadequacy of the models. Lastly we discuss a possibility of constraining the inclination angle (and hence the loop shape) with spatially-unresolved soft X-ray line spectra which are Doppler-shifted due to plasma upflows. |
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