Interferometric observations to analyze circumstellar environments and planetary formation

Protoplanetary disks have a rich structure, with different physics playing a role in different regions of the disk. They are under constant evolution, due to a combination of various physical and chemical processes, e.g., accretion, photo-evaporation, gas-dust interactions, grain growth, and the interaction with protoplanets. The dynamic ranges involved span orders of magnitudes on spatial scales, orbital times, temperatures, and dust- or gas-densities. The extreme dynamic ranges involved in the structure and composition of these objects mean that very different observational techniques have to be combined together to probe their various regions. This work makes use of new interferometric and spectroscopic measurements in the infrared, together with published mid-infrared images and spectral energy distribution fluxes from UV to mm-wavelength, to instruct a new comprehension of the well-known IRS48 object, and uncover part of the delicate balance of physical processes at stake. This PhD reports the first direct imaging of the full extents of a polycyclic aromatic hydrocarbon and very small grains ring in a young circumstellar disk, presents a revised model for the IRS48 object to explain the rich and complex dust- and gas-environment observed from near-infrared to centimeter wavelengths. Also, the spectral type of the spectroscopic binary MWC361 is determined. This will lead to a precise characterization of the stellar parameters of this binary, opening a new window on the studying of the disappearance of the circumsecondary disk of the binary, while the circumprimary disk is still present. The leitmotif throughout this thesis is the understanding of the last moments of circumstellar disks, and the search for the processes which dissipate them. This particular step of the disk-evolution is one the most mysterious to date, yet it sets critical constraints on the by-product of circumstellar disks, exoplanets

The VAMPIRES instrument: Imaging the innermost regions of protoplanetary disks with polarimetric interferometry

Direct imaging of protoplanetary disks promises to provide key insight into the complex sequence of processes by which planets are formed. However imaging the innermost region of such disks (a zone critical to planet formation) is challenging for traditional observational techniques (such as near-IR imaging and coronagraphy) due to the relatively long wavelengths involved and the area occulted by the coronagraphic mask. Here we introduce a new instrument -- VAMPIRES -- which combines non-redundant aperture-masking interferometry with differential polarimetry to directly image this previously inaccessible innermost region. By using the polarisation of light scattered by dust in the disk to provide precise differential calibration of interferometric visibilities and closure phases, VAMPIRES allows direct imaging at and beyond the telescope diffraction limit. Integrated into the SCExAO system at the Subaru telescope, VAMPIRES operates at visible wavelengths (where polarisation is high) while allowing simultaneous infrared observations conducted by HICIAO. Here we describe the instrumental design and unique observing technique and present the results of the first on-sky commissioning observations, validating the excellent visibility and closure phase precision which are then used to project expected science performance metrics

Observations interférométriques pour l'analyse des environnements circumstellaires et de la formation planétaire

The dust- and gas-rich disks surrounding numerous pre-main-sequence stars are of key interest for unveiling how planetary system are formed; they are the initial conditions for planetary formation. Protoplanetary disks have a rich structure, with different physics playing a role in different regions of the disk. The dynamic ranges involved span two to five orders of magnitudes on spatial scales, orbital times, temperatures, and much more in dust- or gas-densities. The extreme dynamic ranges involved in the structure and composition of these objects mean that very different observational techniques have to be combined together to probe their various regions.This PhD makes use of new K, L and M-band imaging and Sparse-Aperture-Masking (SAM) Interferometric measurements, 3-4 micron spectroscopy, together with published 8.6 and 18.7 micron images and spectral energy distribution (SED) fluxes from UV to mm-wavelength to instruct a new comprehension of the famous IRS-48 object, and uncover the delicate balance of physical processes at stake.This PhD reports the first ever direct imaging of the full extents of a polycyclic aromatic hydrocarbon (PAH) and very small grains (VSG) ring in a young circumstellar disk, presents a revised model for the IRS-48 object to explain the rich and complex dust- and gas-environment observed from near-infrared to centimeter wavelengths, and sets limits on how much silicates grains - hence replenishment - is to be expected in the PAH and VSG ring.Radiative transfer modelling of the disk-structure and grains compositions converges to a classical-grains outer-disk from 55 AU combined with an unsettled VSG & PAH-ring, where the inner- and outer-rim are resolved: 11 and 26 AU. A brighter hence larger central-star with modified extinction parameters accounts for the near-infrared flux observed in the SED: the inner-most disk at ~1 AU is not needed. The revised stellar parameters place this system on a 4 Myr evolutionary track, much younger than the previous estimations, in better agreement with the surrounding region and disk-dispersal observations. Using closure-phases, two over-luminosities are found in the PAH-ring, at color-temperatures consistent with the radiative transfer simulations; one follows a sub-Keplerian circular orbit. This PhD also shows that only very few settled thermal silicates can be co-located with the PAH-ring, with a depletion factor of ~5-6 compared to classical circumstellar dust-to-PAH abundances. A ~3 Jupiter-masses companion on a 40 AU orbit is compatible with the new disk structure and the previous mm-grains asymmetry.The IRS-48 disk is found to be void of dust-grains in the first 55 AU, except for a 3.7e-10 Solar-masses of a mixture of ionized and neutral PAH, and VSG. This places IRS-48 at the final stage of transition disks, when photo-evaporation dominates the disk evolution and eventually causes dispersal. Given the highly radiating environment, this PhD also highlights the probable replenishment of the inner PAH & VSG-ring through the channeling of such particles from the outer reservoir, due to the on-going accretion on the companion.La poussière et le gaz qui entourent beaucoup d'étoiles jeunes sont d'un intérêt critique pour comprendre la formation planétaire ; ils représentent les conditions initiale de la formation planétaire. Les disques proto-planétaire ont une structure riche, avec différents processus physiques à l'oeuvre dans différentes régions du disque. Les grandeurs en jeu s'étalent sur 2 à 5 ordres de grandeur en échelles spatiales, période orbitale, températures, et bien plus en ce qui concerne la densité de gaz et poussière. Les variations extrêmes de ces paramètres clés impliqués dans la structure et la compositions de ces objets implique nécessairement l'utilisation combinée de différentes techniques d'observation.Cette recherche se base sur l'utilisation de nouvelles données d'imagerie et de masquage de pupille (SAM) en bandes K, L et M, de spectres entre 3 et 4 microns, en plus d'images à 8.6 et 18.7 microns et de données de densité spectrale de flux (SED) issus de la littérature. Ces données des UV aux longueurs d'ondes millimétriques ont permis de construire une nouvelle compréhension de l'objet IRS-48, et de mettre en avant l'équilibre subtil des processus physiques en jeu. Ce travail a permis d'imager pour la première fois l'intégralité spatiale d'un disque composé d'hydrocarbures polycyclique aromatique (PAH) et de très petits grains (VSG) autour d'un objet stellaire jeune. Il propose un modèle révisé pour cet objet de façon à expliquer l'environnement riche et complexe de gaz et poussières observé en proche infrarouge et en ondes millimétriques, et pose des limites sur la quantité attendue de grains silicatés - synonymes de renouvelle du disque - qui peut se trouver dans ce disque de PAH/VSG.Une modélisation en transfert radiatif de la structure du disque et de la composition des grains converge vers un disque externe à 55 AU composé de grains classiques, en plus d'un disque non-sédimenté de PAH et VSG dont les bords internes et externes sont résolus: 11 et 26 AU. Une étoiles plus brillante - donc plus large - associée à une adaptation des courbes de rougissement permet d'expliquer les flux observés dans le proche-infrarouge: le disque très interne à l'étoile, à 1 AU environ, n'est plus nécessaire. Les nouveaux paramètres stellaire permettent d'estimer un âge de 4 millions d'années pour cet objet, beaucoup plus jeune que les estimations précédentes, et en meilleur accord avec l'environnement direct de l'étoile et les statistiques de dispersion de tels disques. L'utilisation de clôtures de phase a permis de détecter deux sur-brillance au sein du disque de PAH, dont la température de couleur correspond à la température de ce disque trouvé grâce au transfert radiatif. Une sur-brillance suit une orbite circulaire sous-Keplerienne. Ce travail a permis de montrer qu'une quantité limitée de grains classiques silicatés pouvait être localisé dans le disque de PAH, avec un facteur de déplétion de 5-6 par rapport aux abondances classiques de poussière-à-PAH. Un compagnon d'environ 3 masses de Jupiter sur une orbite à 40 AU est compatible avec la nouvelle structure du disque et l'observation précédente d'une asymétrie de grain millimétriques.Le disque d'IRS-48 est dépourvu de poussière dans ses premiers 55 AU, à l'exception de 3.7e-10 masses solaire d'une mixture de PAH neutres et ionisés, et de VSG. Ceci place IRS-48 au stade final des disques de transition, alors que la photo-evaporation commence à dominer l'évolution du disque jusqu'à provoqué sa dispersion. Etant donné le fort environnement radiatif, the doctorat permet aussi de mettre en avant un probable renflouement du disque interne de PAH et VSG par le disque externe grâce à des effets gravitationnels induits par le compagnon

Predicting exoplanet observability in time, contrast, separation, and polarization, in scattered light

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Sparse aperture masking with SPHERE

International audienceSparse Aperture Masking (SAM) has recently been commissioned on SPHERE, the VLTs new adaptive optics high resolution imager. SAM extends the capabilities of SPHERE by providing high contrast measurements at and beyond the traditional diffraction limit. SAM can be used in conjunction with each of the SPHERE modules (IRDIS, IFS and ZIMPOL), allowing dual band imaging in the visible and near-infrared, near-infrared integral field spectroscopy, and polarized differential imaging in the visible and near-infrared. In this paper we report information relevant for observers as well as some commissioning observations

A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48

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Molecular and Functional Diversity of Histamine Receptor Subtypes

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