Caractérisation d'un coronographe pour la détection d'exoplanètes avec MIRI/JWST

Abstract : Since the first discovery of an exoplanet in 1995 around a main sequence star, many projects have been deployed with the goal to detect extrasolar planets. At this time, most planets have been discovered by indirect means. Indeed, direct detection is made very difficult because both a very high contrast between the star and the planet and a very high angular resolution are needed. A solution to this problem is coronagraphy. A coronagraph is an instrument designed to attenuate the flux of the star by reducing the instrumental diffraction. I have studied this system for two different instruments, with two very different approaches. I have first studied the four quadrant phase mask coronagraph of MIRI (``Mid-InfraRed Instrument''), an instrument of the JWST (``James Webb Space Telescope''). The main objective of this instrument is to detect Jupiter-like planets. I have constributed to the control test of coronographic components. Then I focused on coronagraphic simulations. In this context, I have established the statistical properties of exoplanet detectability around the nearest stars. Then I have estimated the pointing limitations in coronagraphic mode. Besides, I have specified the on-board algorithms and the pointing procedures. Another method which can be used to detect exoplanets on the JWST is the transit method. I have studied it in the peculiar case of a primordial Earth considering two instruments of the JWST. In a second time, I focused on the direct detection of Earth-like planets with a coronagraphic device on the ELTs (``Extremely Large Telescope''). The flux contrast between the star and the planet is $2.10^{-10}$ in the near infrared. I have studied from an analytical and numerical point of view the interest of a simultaneous differential imaging after the coronagraph. I have quantified the impact of static aberrations and the requirement on optical quality. Another constraint is set by the photon noise. The level of this photon noise is imposed by the adaptive optics; consequently, I have studied an ELT at the dome C where the turbulence is less important and thus, where the correction is larger. At last, I have underlined the additionnal limitations brought by real coronographs and by a simultaneous spectral calibration.
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Astrophysics [astro-ph]. Université Paris-Diderot - Paris VII, 2007. French


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Submitted on : Thursday, February 14, 2008 - 9:47:31 AM
Last modification on : Thursday, February 14, 2008 - 10:37:38 AM

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Céline Cavarroc. Caractérisation d'un coronographe pour la détection d'exoplanètes avec MIRI/JWST. Astrophysics [astro-ph]. Université Paris-Diderot - Paris VII, 2007. French. <tel-00255764>

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