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Développement et exploitation scientifique d’un nouvel instrument interférométrique visible en optique guidée

Abstract : Long baseline visible interferometry in astronomy is an observing technique which allows to get insights of an object with an outstanding angular resolution, unreachable with single-dish telescope. Interferometric measurements with ground-based instrumentation are currently limited in sensitivity and precision due to atmospheric turbulence. However, the new astrophysical needs, particularly the determination of fundamental parameters or the study of the closed environment and the surface of the stars, require to observe fainter objects with a better precision than now in visible interferometry. Ought to overcome the atmospheric turbulence, multispeckle interferometry has been developed by adapting speckle imaging technics used on single-dish telescope. Today, in order to improve the performance of the future combiners, instrumentation progresses to the use of a new generation detector called EMCCD, and the use of optical fibers which are coupled with adaptive optics. This path is chosen thank to the success of the use of the adaptive optics with the fringe tracking in the infrared interferometry in 2017 (Gravity Collaboration et al. 2017), in order to compensate turbulence. FRIEND prototype (Fibered and spectrally Resolved Interferometer - New Design) has been designed to characterize and estimate the performance of such a combination of technologies, in the visible spectral band. The improvement of the precision of the measurements from interferometric instruments is due to optical fibers and the dynamical range of the EMCCD. The counterpart of using the optical fibers is a loss in sensitivity due to a low injection rate of flux into the fibers because of the atmospheric turbulence. On the other hand, sensitivity is improved thanks to adaptive optics and EMCCDs. Indeed, adaptive optics increases the injection rate and EMCCDs can measure low fluxes. Lastly, FRIEND is a pathfinder for the future instrument SPICA which should recombine up to 6 telescopes (Mourard et al. 2017, 2018). Fringe-tracking aspects will have to be studied for SPICA; this topic is not dealt with in this thesis. In this work, I present the FRIEND prototype, which can recombine up to three telescopes and operates in the R band with dispersed fringes. It has Gaussian polarization-maintaining single mode optical fibers and an EMCCD. It is set up at the Center for High Angular Resolution Astronomy (CHARA), at Mount Wilson, in California. CHARA is currently being equipped with adaptive optics. I develop estimators of visibility modulus and closure phase, the data reduction software and an observing strategy. Thanks to that, I am able to show that adaptive optics improves the injection rate. I also demonstrate how important the stabilization of injection is to maximize the signal-to-noise ratio (SNR) per frame. Birefringence of the fibers decreases the performance of the instrument but we manage to compensate it. I show how such an instrument can measure low visibility with a better precision than now by developing and using a SNR model of FRIEND. Finally, FRIEND has entirely been tested on the known binary system ζ Ori A. These observations demonstrate how reliable and accurate the measurements of FRIEND are.
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Marc-Antoine Martinod. Développement et exploitation scientifique d’un nouvel instrument interférométrique visible en optique guidée. Astrophysique [astro-ph]. Université Côte d'Azur, 2018. Français. ⟨NNT : 2018AZUR4215⟩. ⟨tel-02023685⟩

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