Academic literature on the topic 'Exoplanètes – Imagerie spectroscopique'
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Dissertations / Theses on the topic "Exoplanètes – Imagerie spectroscopique":
Alagao, Mary Angelie. "Characterization and optimization of the Evanescent Wave Coronagraph." Electronic Thesis or Diss., Saint-Etienne, 2023. http://www.theses.fr/2023STET0060.
Direct imaging of exoplanets remains challenging due to the high contrast and the small angular separation between the star and the planet. It requires suppressing the blinding glare from the star and ensuring that the planet's faint light is not buried deep in various noises. Successful detection depends on the technological readiness and maturity of techniques and algorithms employed while considering the significant trade-offs on raw contrast, inner working angle, and throughput. One of its key components is the use of coronagraphs – instruments with the sole purpose of blocking/reducing the light from the star. This work presents a new type of Lyot coronagraph, invented by Dr. Yves Rabbia, that relies on the frustrated total internal reflection (FTIR) principle to suppress the starlight. This coronagraph is aptly called the Evanescent Wave Coronagraph (EvWaCo) owing to its nature that its focal plane mask, comprising a lens and a prism, reflects the off-axis source (planet) and transmits the on-axis source (star) by capturing the evanescent waves. This thesis aims to provide the reader with the groundwork that highlights EvWaCo's three main advantages: i) the mask is inherently achromatic, ii) the size of the mask is adjustable by changing the pressure between the lens and the prism, and iii) both the stellar light and the planet light can be collected simultaneously for low-order wavefront sensing, and proper stellar light centering. The performance of EvWaCo is assessed through experiments in a laboratory and then compared to numerical simulations. The experimental results show a raw contrast equal to a few 10-4 at 3 ��/�� over the full I-band (��c = 800 nm, ∆��/�� ≈ 20%) and at 4 ��/�� over the full R-band (��c = 650 nm, ∆��/�� ≈ 23%). The simulations confirm the achromatic rejection capability of EvWaCo as it showed a raw contrast of 10-4 at the same radial distance over both bandpasses. This thesis concludes with the status of its testbed and future perspectives
Bhowmik, Trisha. "Spectroscopie résolue de disques debris avec SPHERE/VLT." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEO019.
Debris disks are found around many young main-sequence stars. They are characterized by the dusty, gas-depleted environment as opposed to gas-rich protoplanetary disks. Debris disks are also considered as `secondary disks' because they bear non-primordial dust grains which are constantly generated by continuous collisions of planetesimals. Recent observations in the sub-millimeter have shown compelling evidence that a significant amount of gas can be present in some of these disks.High-contrast and high-resolution imaging have proven to be very effective to observe debris disks and to resolve their morphological structures, tracing the distribution of the small dust grains. Scattered light imaging in the near-infrared can measure the intensity distribution of the disk, which is related to the grain properties. The disk intensity varies differently in total intensity imaging and polarimetric imaging so it is necessary to use both to better constrain dust characteristics.Considering the advantages of high-contrast imaging, I aimed to study the scattered light images of debris disks obtained by one such instrument, the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) which is installed at the VLT in Chile. To obtain a post-processed intensity image with reduced stellar residuals in a post-adaptive optics coronographic observation, the angular differential imaging (ADI) and polarimetric differential imaging (PDI) techniques are usually performed but imply self-subtraction which must be corrected for to recover true photometry. In order to model debris disks, I used a radiative transfer module, GRaTer and processed disk synthetic images through equivalent post-processing technique as the data, from which the morphology of the disk and its grain-size distribution is constrained.The goal of my thesis is to interpret spectral and temporal variations of debris disks, both in terms of their morphology and grain-size distribution to finally understand planet formation. To achieve this I studied the morphology of the debris disk HD32297 and developed a model mimicking the density and intensity distribution of the disk. This model then was used to retrieve the surface brightness and average reflectance of the disk. The average reflectance was then compared to a spectrum obtained from analyzing the particle size distribution within the disk for different grain compositions. Fitting the spectra to the average reflectance provided an important result, which indicated that the minimum grain size is well below blow-out size independent of the grain composition. The possible explanations which were looked into for the presence of sub-micron grains are a combination of a steady-state collisional cascade, collisional avalanche mechanism and gas drag due to the presence of a large quantity of gas in this debris disk. In second part of the thesis I applied similar work to debris disk HD106906 and HD141569 in total intensity. For HD106906 the visible flux asymmetry between the two sides of the disk was modeled and resolved and for HD141569 using aperture photometry a spectral analysis of the particular structure compared to the full southern part of the inner disk was performed. In perspective, this work will open a more systematic analysis of the many multi-wavelength observations obtained with high-contrast imaging of debris disks in order to understand the evolution of grains to planets
Bonnefoy, Mickaël. "Recherche et caractérisation des propriétés physiques et chimiques des compagnons de faible masse, naines brunes et planètes géantes, à l'aide d'observations à haut contraste et à haute résolution angulaire." Grenoble, 2010. http://www.theses.fr/2010GRENY035.
My work takes place in the dynamic context of the direct detection of low mass companions (brown dwarfs, extrasolar planets). I intent to characterize their physical and chemical properties, and to understand the mechanisms that lead to their formation and drive their evolution. This requires using high contrast and high angular resolution techniques in order to resolve the close environment of the stars without being limited by their flux. I had the opportunity to participate to observational campaigns so as to detect new sources. I developed a set of data analysis tools designed to extract the spectra and the flux of the objects into photometric bands. Finally, I used this information to study the physical (radius, mass, age) and the atmospheric (composition, effective temperature, surface gravity) properties of these objects. The first part of this manuscript focus on the detection of young (age < 100 Myrs) low mass companions using imaging. I describe a set of reduction and analysis tools dedicated to the angular differential imaging technique. These tools have been used on data coming from the NaCo instrument located on the Very Large Telescope (Chile). They allowed re-detecting the extrasolar planet β Pictoris b. This companion is closer to its star than any of the extrasolar planets detected directly so far. This discovery brings the definite proof that giant planets can form in less than 12 million years within disks. I finally present a complementary analysis I conducted to initiate the characterization of this valuable object. The determination of the spectroscopic properties of young and low mass objects in the near infrared (1. 1-2. 5 µm) constitutes the second aspect of my work (and is reported in the last part of the manuscript). I started developing analysis and processing tools dedicated to data gathered on the adaptive optics assisted integral field spectrograph SINFONI. These efforts were used to analyze the spectrum of the planet/brown dwarf companion AB Pic b. This work was pursued to built a spectral library of young objects. This library brings a collection of reference spectra, necessary for the study of other young companions. It also brings new constraints on the latest generation of atmospheric models of cool objects. To conclude, I used the instrument NaCo and SINFONI to characterize the binary system TWA 22AB that could calibrate evolutionary models of low mass objects
Delorme, Jacques-Robert. "Imagerie haute dynamique en larges bandes : coronographie et minimisation des tavelures en plan focal." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC294/document.
Among the 3000 exoplanets detected at this time, about 50 have been observed by direct imaging. The benefit of direct imaging is to give access to exoplanet light, paving the way for spectroscopic study of their atmospheres and surfaces. Moreover, direct imaging is also the only method that enables the study of exoplanets located in the outer parts of the stellar systems as well as circumstellar disks, which are fundamental to understand the different stages of planetary formation. However, there are two challenges : the small angular separation between an exoplanet and its star (less than a fraction of 1’’), and the contrast between the two objects which is of the order of 10-4 in near infrared for young Jupiter and of the order of 10-10 in visible light for Earth like planets. Existing instruments use coronagraphs to filter light from the host star and observe its tenuous neighborhood. They also use active techniques in order to minimize, in the final image, the brightness of speckles induced by wavefront aberrations. Coupled with differential imaging techniques, these instruments led to the discovery and study of young and massive exoplanets and circumstellar disks. However, to detect fainter exoplanets closer to their star, imaging techniques are now at the heart of an active research. For example, the Paris Observatory developed the banc très haute dynamique (THD bench) aiming at testing several high contrast imaging techniques and their associations as the four quadrants phase masque (FQPM) and the self-coherent camera (SCC) which is a focal plane wavefront sensor.At the beginning of my PHD, I mainly focused my work on the development and the study of coronagraphs and focal plane wavefront sensors able to work in broadband (between 12,5 % and 40 %). I tested on the THD bench two coronagraphs, the multi four-quadrant phase-mask (MFQPM) and the dual-zone phase-mask (DZPM). I proved that the DZPM is able to reach contrasts of 4 10-8 at angular separations ranging from 7 to 16 λ/D using a spectral bandwidth of 250 nm centered on 640 nm (40 %). I also developed and tested a new version of the SCC, less sensitive to chromatism, called the multireference self-coherent camera (MRSCC). By combining both DZPM and MRSCC, I reached in closed loop contrasts of 4.5 10-8 between 5 and 17 λ/D for a spectral bandwidth of 80 nm centered on 640 nm (12,5 %). These two results are important because they show that it is possible to build an instrument able to reduce the stellar light and actively control optical aberrations directly from a scientific image registered in a large spectral bandwidth which is requiered for the next generation of instruments. During my PHD, we also strated a collaboration to install the SCC at the Palomar Observatory. During two missions in which I took part, we proved, for the first time, that the SCC can be associated with a vortex coronagraph. Finally, based on these results, we plan to demonstrate the SCC concept on sky in the fall of this year
Bruno, Giovanni. "Characterization of transiting exoplanets : analyzing the impact of the host star on the planet parameters." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4746/document.
During my PhD, I analyzed the spectra of nine Kepler stars obtained by radial velocity (RV) observations. This allowed the characterization of their planetary companions. I analyzed the spectra of twenty-one other CoRoT and Kepler stars, likely orbited by low-mass M dwarfs. This helped widening the sample of low-mass stars with measured mass and radius. I calculated the chromospheric activity indfex of thirty-one stars observed with SOPHIE/OHP, helping the study of star-planet interactions. I studied the behavior of SOPHIE in low signal-to-noise ratio (SNR) regime. I determinhed the SNR range in which a stellar spectrum is reliable for the measure of the stellar parameters.Within the SOPHIE consortium, I followed the complete analysis of the Kepler-117 system. This multi-planetary system presents variations in the planetary orbital periods due to their mutual dynamical interacion (TTVs). To fit the system parameters, a specific fitting approach including TTV modeling was developed. We derived the system parameters by the simultaneous fit of transits, RVs, and TTVs (Bruno et al. 2015).Finally, I addressed the problem of stellar activity in transit photometry. I implemented two starspot modeling codes into an MCMC algorithm, adding spot evolution to oneof them. I applied the codes to the Sun, CoRoT-7, and CoRoT-2. I carried an extensive study on the light curve of CoRoT-2, and explored the effects of the spots on the transit parameters (Bruno et al., in prep.). With the FF’ method (Aigrain et al. 2012), I contributed to explore the connection between the photometric and RV signature of starspots in CoRoT-7
Lavigne, Jean-Francois. "Imagerie à haut contraste et caractérisation d'exoplanètes par la spectroscopie intégrale de champ." Thèse, 2009. http://hdl.handle.net/1866/3456.
The main goal of this thesis is the improvement of high-contrast imaging techniques enabling the direct detection of faint companions at small separations from their host star. More precisely, it answers some questions linked to the development of the Gemini Planet Imager (GPI), a second generation instrument for the Gemini telescopes. This instrument will use an integral field spectrometer (IFS) to characterize the detected faint companions and to attenuate the speckle noise limiting their detection. Moreover, it will use a combination of two deformable mirrors, the woofer and the tweeter, in its adaptive optics (AO) system in order to reach the atmospheric turbulence correction sought. The woofer corrects the low spatial frequency high amplitude aberrations while the ones with a high frequency and a low amplitude are compensated by the tweeter. First, the high-contrast imaging performance achieved by current on-line IFS on 8-10 m telescopes are investigated through the observation of the faint companion to the star GQ Lup using the IFS NIFS and the AO system ALTAIR presently in function on the telescope Gemini North. The angular differential imaging (ADI) technique is used to reach an attenuation of the speckle noise by a factor of 2 to 6. The JHK spectra obtained were used to constrain the mass of the companion to 8−60 MJup making it most likely a brown dwarf. MJup represents the mass of Jupiter. Current on-line IFS were conceived to be versatile so that they could be used in many astrophysical fields. Hence, their conception was not optimized for high-contrast imaging. The second part of this thesis objective was to build and test in the laboratory an IFS optimized for this task. Four speckle suppression algorithms were tested on the resulting data: the simple difference, the double difference, the spectral deconvolution and a novel algorithm developed in this thesis dubbed the spectral twin algorithm. We found the spectral twin algorithm to be the most efficient to detect both types of companions tested: methanated and non-methanated. The detection signal-to-noise ratio was improved by a factor up to 14 for the methanated companion and up to 2 for a non-methanated one. In the last part, problems linked to the wavefront correction split between two deformable mirrors are investigated. First, a method allowing to select the woofer key parameters such as its diameter, its number of actuators and its required stroke which influenced the overall instrument design is presented. Second, since GPI will use a Fourier reconstructor, we propose to split the command in the Fourier domain and to limit the modes sent to the woofer to the ones it can accurately reproduce. In GPI, this results in replacing two matrices of 1600×69 elements in the case of a classic command split scheme by a single matrix of 45×69 components with the proposed method.
Bonnefoy, Mickaël. "Recherche et Caractérisation des Propriétés Physiques et Chimiques des Compagnons de Faible Masse, Naines Brunes et Planètes Géantes, à l'aide d'observations à Haut Contraste et à Haute Résolution Angulaire." Phd thesis, 2010. http://tel.archives-ouvertes.fr/tel-00555496.