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Spectropolarimétrie stellaire UV et visible depuis l'espace

Abstract : Over the last few decades, magnetic fields have been detected in almost all kinds of stars. This led to innovative studies on the mapping of magnetic fields and their impact on the circumstellar environment. To go further, we need to use spectroscopy and polarimetry together, in the UV and visible range. The UV domain is used to study the stellar wind and stellar environment, whereas the visible range allows to study the surface of the star. UV+visible spectropolarimetry enables the global study of magnetospheres. This has to be done over at least one rotation period of the star. Therefore, we need to go to space in order to see the UV range and to obtain uninterrupted observations on a complete stellar rotation period. The international consortium UVMag has been created in 2010 to discuss, study and promote a space mission for the study of stellar magnetospheres using simultaneous UV and visible space spectropolarimetry. From the technical point of view, pure spectroscopy in space, both in the UV and visible ranges, has already been successfully used, for example on IUE, and would be very efficient with current detectors and technologies. On the other hand, the UV+visible spectropolarimeter is the most ambitious instrumental challenge for a future space mission. Indeed, until now, no such optical spectropolarimeter has flown on a space mission, despite the fact that the French (particularly the LESIA and IRAP laboratories) are the specialists for such instruments (such as ESPaDOnS at CFHT or Narval at TBL). The first part of my thesis consisted in elaborating the optical design of the polarimetric module for the spectropolarimeter of the space mission Arago, in the framework of the UVMag consortium. I studied various innovative concepts that could be adapted to the specific constraints of this instrument. The specifications indeed show the need for a unique polarimeter covering the complete spectral range [119-888] nm. Moreover, the usual compacity, lightness and robustness constraints of a space instrument are added to these specifications. I focused my work on 2 different polarimeter concepts, a first one based on the polarimetric module of the X-shooter instrument using a temporal modulation and an achromatization of the extraction efficiencies of the Stokes parameters, and a second one based on spatial modulation of the polarization, offering a static polarimeter. I adapted these 2 concepts to the specific constraints of Arago and integrated them to the complete optical design of the instrument. The first concept, using temporal modulation, has been chosen as the baseline for the instrument proposed to ESA for the Cosmic Vision calls M4 and M5. The goal was then to demonstrate the feasibility of the two concepts.
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Martin Pertenais. Spectropolarimétrie stellaire UV et visible depuis l'espace. Astrophysique stellaire et solaire [astro-ph.SR]. Université Paul Sabatier - Toulouse III, 2016. Français. ⟨NNT : 2016TOU30252⟩. ⟨tel-01581927⟩

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