Étude des nébuleuses spirales de poussière autour des étoiles Wolf-Rayet

Abstract : Massive stars are one of the major contributors to the enrichment of galaxies in heavy elements and interstellar dust. The last stage of their evolution is represented by the Wolf-Rayet phase (WR). WR stars generate a dense radiative stellar wind, which can interact with the wind from a close companion and cause a spiral dust environment called pinwheel nebula. The orders of magnitude associated with this kind of object are spectacular: with a dust formation rate equivalent to the mass of the planet Mars produced each year, WR stars compete with the historical dust producers, like the stars of the asymptotic giant branch (AGB) or the supernovae (SN). Dusty WR stars could thus answer a well-known problem: where does the dust observed in galaxies come from? This thesis aims at enriching our knowledge about this problem using all aspects of the scientific chain: from observation to data analysis by using different levels of sophistication in numerical modelling (analytical, radiative transfer and hydrodynamics). The first aspect explored by this thesis concerns the modelling of spiral dust nebulae. I first developed an analytical model for the spiral to constrain the geometrical aspects of the spiral, including a number of physical hypothesis like the dust sublimation radius and different types of internal structure. The next step consisted to include the radiative transfer in the geometrical model in order to link the intensity distribution of the object (the image) to its density distribution. This 3-D model of spiral allow to study the opacity and shadowing effects related to the dust mass considered. Similarly, I developed a 3-D axisymmetric radiative transfer model to mimic the spiral into a series of concentric rings. This model aims to reproduce the intensity distribution of a spiral at a given azimuth and allows a direct comparison with the radial intensity profiles derived from observations. Finally, we implemented a 3-D hydrodynamic model of a wind-wind interacting binary to get a realistic idea of the physical conditions in places around the dust nucleation zone. The second aspect addressed by this thesis focuses to the study of the prototype of the pinwheel nebula, called WR104. Such object is an ideal laboratory to study the problem of dust nucleation around massive stars. I explored all spatial scales of WR 104: From the large scale with VLT/VISIR to study the link with the interstellar medium, to the internal regions with VLTI/AMBER to probe the dust nucleation zone, including intermediate angular resolution to study the pinwheel structure with extreme adaptive optics instrument VLT/SPHERE. The third and last aspect deals with the second generation of the instrument installed at the European Very Large Telescope Interferometer (VLTI): MATISSE. It is the first instrument operating simultaneously in the L, M and N bands by recombining the light coming from four telescopes. MATISSE was developed to study different scientific cases: protoplanetary disks, the circumstellar environments and the active galactic nuclei. To prepare the first observation programs, I developed an automated tool, called PREVIS, to determine the observability of objects according to their magnitude and celestial coordinate. In the context of spiral nebulae, I explored the image reconstruction capabilities of the instrument by testing different aspects: geometric (size, inclination, opening angle, etc.) and observational (coverage (u-v), sampling). The unprecedented spatial resolution of MATISSE of 3 mas at 3.5 µm will allow to study these objects in a unique way, resolving for the first time the thickness of the spiral arm, its internal structure or the exact position of the sublimation radius.
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Anthony Soulain. Étude des nébuleuses spirales de poussière autour des étoiles Wolf-Rayet. Astrophysique [astro-ph]. Université Côte d'Azur, 2018. Français. ⟨NNT : 2018AZUR4245⟩. ⟨tel-02310068⟩

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