Détermination de la structure tridimensionnelle de la couronne solaire à partir d'images des missions spatiales SoHO et STEREO

Abstract : The influences of the Sun on Earth is the source of new developments in astrophysics regrouped under the name of space weather. The solar wind takes an important part in these interactions, especially the fast solar wind which comes from the solar poles. Thus, we underdstand the importance of the study of the Sun polar regions. In this thesis, we will analyse the plumes located at the poles which may be the source of the fast solar wind. The method we will use could be used to study the Coronal Mass Ejections too. We will use the data acquired by the space missions SoHO and STEREO. Those missions give away measurments of the solar light emission in the extreme ultraviolet (EUV) and coronographic data in visible light. For volumic reconstructions of the corona it is important that the two STEREO spacecraft have almost identical instruments. And they are very similar to the SoHO spacecraft. Thus, we have three simultaneous viewpoints. We developed a method which can at the same time perform a threedimensional reconstruction of the emission and estimate the temporal evolution of plumes while making use of the simultaneous viewpoints. This is possible thanks to the development of a model of evolution of the polar plumes. In this model, we assume that the plumes do not move but have a varying intensity. By first defining the positions of the plumes, we obtain a bilinear problem with a static emission set and a temporal set of unknowns. We applied this method to simulated data and to EUV data as measured by SoHO and STEREO. The simulations showed us the importance to take into account all the geometric parameters of the space missions. We developed a projector backprojector code which takes into account all these parameters. Thanks to a study on simulations we defined the parameters which minimize the artifacts of reconstruction. Finally, thanks to the three bandwidth of EUV data, we can perform a spectral study of the reconstruction, avoiding the line of sight integration. Using a model that link the plasma parameters and the spectral variation of the emission we can estimate the density and the electronic temperature for each voxel of the three-dimensional maps of the corona. To conclude, the future availabilty of data from the SDO mission will allow us to improve the spectral reconstructions thanks to the presence of eight bandwidth in the EUV. We will investigate future developments in the automatic estimation of the temporal evolution areas and in the reconstruction of CME.
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Submitted on : Monday, January 18, 2010 - 4:55:09 PM
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Nicolas Barbey. Détermination de la structure tridimensionnelle de la couronne solaire à partir d'images des missions spatiales SoHO et STEREO. Astrophysique [astro-ph]. Université Paris Sud - Paris XI, 2008. Français. ⟨tel-00448329⟩

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