High-contrast imaging instruments such as GPI and SPHERE are discovering gap structures in protoplanetary disks at an ever faster pace. Some of these gaps may be opened by planets forming in the disks. In order to constrain planet formation models using disk observations, it is crucial to find a robust way to quantitatively back out the properties of the gap-opening planets, in particular their masses, from the observed gap properties, such as their depths and widths. Combining 2D and 3D hydrodynamics simulations with 3D radiative transfer simulations, we investigate the morphology of planet-opened gaps in near-infrared scattered-light images. Quantitatively, we obtain correlations that directly link intrinsic gap depths and widths in the gas surface density to observed depths and widths in images of disks at modest inclinations under finite angular resolution. Subsequently, the properties of the surface density gaps enable us to derive the disk scale height at the location of the gap h, and to constrain the quantity M-p(2)/alpha, where Mp is the mass of the gap-opening planet and a characterizes the viscosity in the gap. As examples, we examine the gaps recently imaged by VLT/SPHERE, Gemini/GPI, and Subaru/HiCIAO in HD 97048, TW Hya, HD 169142, LkCa. 15, and RX J1615.3-3255. Scale heights of the disks and possible masses of the gap-opening planets are derived assuming each gap is opened by a single planet. Assuming a = 10(-3), the derived planet masses in all cases are roughly between 0.1 and 1M(J).

Stars form via the gravitational collapse of molecular clouds during which time the protostellar object contracts by over seven orders of magnitude. If all the angular momentum present in the natal cloud was conserved during collapse, stars would approach rotational velocities rapid enough to tear themselves apart within just a few Myr. In contrast to this, observations of pre-main sequence rotation rates are relatively slow (∼ 1 − 15 days) indicating that significant quantities of angular momentum must be removed from the star. I use observations of fully convective pre-main sequence stars in two well-studied, nearby regions of star formation (namely the Orion Nebula Cluster and Taurus-Auriga) to determine the removal rate of stellar angular momentum. I find the accretion disc-hosting stars to be rotating at a slower rate and contain less specific angular momentum than the disc-less stars. I interpret this as indicating a period of accretion disc-regulated angular momentum evolution followed by near-constant rotational evolution following disc dispersal. Furthermore, assuming that the age spread inferred from the Hertzsprung-Russell diagram constructed for the star forming region is real, I find that the removal rate of angular momentum during the accretion-disc hosting phase to be more rapid than that expected from simple disc-locking theory whereby contraction occurs at a fixed rotation period. This indicates a more efficient process of angular momentum removal must operate, most likely in the form of an accretion-driven stellar wind or outflow emanating from the star-disc interaction. The initial circumstellar envelope that surrounds a protostellar object during the earliest stages of star formation is rotationally flattened into a disc as the star contracts. An effective viscosity, present within the disc, enables the disc to evolve: mass accretes inwards through the disc and onto the star while momentum migrates outwards, forcing the outer regions of the disc to expand. I used spatially resolved submillimetre detections of the dust and gas components of protoplanetary discs, gathered from the literature, to measure the radial extent of discs around low-mass pre-main sequence stars of ∼ 1−10 Myr and probe their viscous evolution. I find no clear observational evidence for the radial expansion of the dust component. However, I find tentative evidence for the expansion ofthe gas component. This suggests that the evolution of the gas and dust components of protoplanetary discs are likely governed by different astrophysical processes. Observations of jets and outflows emanating from protostars and pre-main sequence stars highlight that it may also be possible to remove angular momentum from the circumstellar material. Using the sample of spatially resolved protoplanetary discs, I find no evidence for angular momentum removal during disc evolution. I also use the spatially resolved debris discs from the Submillimetre Common-User Bolometer Array-2 Observations of Nearby Stars survey to constrain the amount of angular momentum retained within planetary systems. This sample is compared to the protoplanetary disc angular momenta and to the angular momentum contained within pre-stellar cores. I find that significant quantities of angular momentum must be removed during disc formation and disc dispersal. This likely occurs via magnetic braking during the formation of the disc, via the launching of a disc or photo-evaporative wind, and/or via ejection of planetary material following dynamical interactions.

Neste trabalho estudamos a dinâmica de discos torcidos finos e espessos para compreender melhor a propagação da deformação nestes discos. No caso dos discos finos, estudamos a física do efeito Bardeen-Petterson e aplicamos este modelo para explicar o jato em escalas de parsec e kilo-parsec da galáxia NGC 1275. Encotramos que o efeito Bardeen-Petterson reproduziu muito bem a forma do jato e com isto derivamos os parâmetros do disco como raio, valores das viscosidades azimutal e vertical, lei de potência da densidade superficial e spin do buraco negro. Para uma melhor compreensão da física destes discos, realizamos simulações GRMHD de discos moderadamente finos tanto planos como inclinados para estudar a evolução do ângulo de inclinação entre os momentos angular do buraco negro e do disco de acresção assim como o ângulo de torção que está associado com a precessão do disco. Encontramos que quando o disco de acresção e o buraco negro rotacionam no mesmo sentido, o ângulo de inclinação entre os momentos angular apresentou um comportamento oscilatório na parte interna do disco e permaneceu constante na parte externa em acordo com as previsões teóricas. Já quando o buraco negro rotacina no sentido oposto ao disco de acresção, encontramos pela primeira vez numa simulação GRMHD evidências de alinhamento, ocorrendo um alinhamento de 10\\% do angulo entre os momentos angulares do disco e buraco negro. Além disso, comprovamos pela primeira vez numa simulação GRMHD a não isotropia do stress. Utilizando um modelo semi-analítico, comparamos os resultados de nossas simulações com este modelo, utilizando os dados da simulações de disco plano como entrada e obitivemos os mesmos comportamentos das simulações tanto no caso prógrado quanto no caso retrógrado mostrando que o alinhamento é devido ao regime onda. / In this work we studied the dynamics of twisted thin and thick disks to better understand how the warp propagates in these discs. In the case of thin discs, we studied the physics of the Bardeen-Petterson effect and we applied this model to explain the shape of the jet in both parsec and kilo-parsec scales of the galaxy NGC 1275. We found that the Bardeen-Petterson effect could explain very well the shape of the jet and with that we derived the disc parameters such as its radius, the values of the kinematic azimutal and vertical viscosities, the power-law of the surface density and the spin of the black hole. To better understand the physics of such discs, we have performed GRMHD simulations of moderatelly thin tilted disks to study the evolution of the tilt angle between the angular momentum of the accretion disk and black hole and also the twist angle which is associated with the precession of the disc. We found that when the accretion disc and the black hole are rotating in the same direction, the tilt angle showed an oscillatory behavior in the inner parts of the disk while in the outer parts it remained constant in agreement with the theorical modelos. However, when both rotate in the opposite direction, we found for the very first time in a GRMHD simulation, evidences of alignment of 10\\% of the tilt angle. Besides that, we prove for the first time in a GRMHD simulation that the stress is far from being isotropic. Using a semi-analitic model, we compared the results of our simulations with this model, using the datas of the untilted simulations as inputs and we found the same behaviors found in the simulations even in prograde case as in the retrograde case showing that the alignment is due to bending waves.

Une manière efficace de contraindre la formation des planètes est l'étude des disques protoplanétaires. Les premières images de ces disques ont été obtenues dans les années 80 en infrarouge et en millimétrique. Ces images dévoilaient pour la première fois la morphologie de l'excès infrarouge vu dans les distributions spectrales d'énergies des étoiles jeunes. Depuis, de nets progrès ont été faits et, outre la détection directe de planètes, nous sommes capables de distinguer les perturbations que celles-ci pourraient engendrer dans ces disques. La région interne de ces disques, où la majorité des planètes sont détectées, est complexe car étant le théâtre de nombreux phénomènes encore mal contraints (sublimation de la poussière, vents, accrétion). Pour les étoiles jeunes les plus proches, observer ces régions revient à atteindre une résolution angulaire de l'ordre de la milliseconde d'arc, inatteignable avec un télescope monolithique. L'interférométrie optique permet de satisfaire cette contrainte. Cette technique consiste à combiner la lumière de deux télescopes ou plus afin de la faire interférer. Ces interférences permettent de contraindre la morphologie de l'objet observé à l'aide de modèles. Mais afin de comprendre les phénomènes en jeu il est nécessaire d'avoir une image indépendante de ces modèles. La reconstruction d'images est possible avec l'avènement récent d'interféromètres à 4 télescopes ou plus. Les premières images ont ainsi pu être reconstruites. Cependant, l'étoile centrale ne permet pas d'accéder facilement à l'image de l'environnement. Ma thèse a donc consisté à outrepasser cette difficulté en développant une méthode de reconstruction d'image adaptée à l'environnement protoplanétaire des étoiles jeunes. Elle consiste à séparer l'étoile centrale de l'image afin de reconstruire son environnement tout en prenant en compte la différence de température entre ces deux éléments. Grâce à cette méthode et aux instruments interférométriques du VLTI, j'ai pu reconstruire les images des premières unités astronomiques d'une douzaine d'étoiles de Herbig et de révéler leurs morphologies. J'ai ainsi pu appliquer une analyse géométrique originale afin de les caractériser. Enfin, j'ai analysé plus en détail un étoile particulière, MWC158, dont j'ai imagé la variabilité qui pourrait être interprétée comme une éjection de matière. Ma thèse démontre l'importance de la prise en compte des aspects chromatiques dans la reconstruction d'image ainsi que de l'adaptation de cette méthode à la spécificité des étoiles jeunes. / An effective way to understand the formation of planets is the study of protoplanetary disks. The first images of these disks were obtained in the infrared and the millimeter in the 80s. These images unveiled for the first time the morphology of the infrared excess seen in the spectral energy distributions of young stellar objects. Since then, significant progress has been made and, in addition to the direct detection of planets, we are able to distinguish the disruption they could cause in these disks. The inner region of these disks, where the majority of planets are found, is complex as being the scene of many phenomena still poorly constrained (dust sublimation, winds, accretion). For the closest young stars, observing these regions amounts to achieve an angular resolution of the order of a milliarcsecond, unattainable with monolithic telescopes. The optical interferometry can reach such a small angle. This technique consists in combining the light of two or more telescopes to make it interfere. These interferences can be used to constrain the morphology of the observed object by using models. But to understand the phenomena involved in the inner parts of young stellar objects, it is necessary to have an independent image. Image reconstruction is possible with the recent advent of interferometers with 4 or more telescopes. The first images were able to be rebuilt. However, the central star does not allow easy access to the environment morphology. The goal of my thesis was to bypass this difficulty by developing a method of image reconstruction which is adapted to the protoplanetary environment of young stars. It consists in separating the central star of the image to reconstruct its environment while taking into account the temperature difference between the two. With this method and the VLTI interferometric instruments, I reconstructed the images of the first astronomical unit of a dozen of Herbig stars and revealed their morphologies. I was able to apply a novel geometric analysis to characterize them. Finally, I have analyzed in more detail a particular star, MWC158, which I imaged the variability that could be interpreted as a matter ejection. My thesis demonstrates the importance of the inclusion of chromatic aspects in image reconstruction and adaptation of this method to the specific characteristics of young stars.

Au delà du système solaire et de ses planètes, nous avons maintenant un catalogue de quasiment 1000 exoplanètes qui illustrent la grande diversité des planètes et des systèmes qu'il est possible de former. Cette diversité est un défi que les modèles de formation planétaire tentent de relever. La migration de type 1 est un des mécanismes pour y parvenir. En fonction des propriétés du disque protoplanétaire, les planètes peuvent s'approcher ou s'éloigner de leur étoile. La grande variété des modèles de disques protoplanétaires permet d'obtenir une grande variété de systèmes planétaires, en accord avec la grande diversité que nous observons déjà pour l'échantillon limité qui nous est accessible. Grâce à des simulations numériques, j'ai pu montrer qu'au sein d'un même disque, il est possible de former des super-Terres ou des noyaux de planètes géantes selon l'histoire de migration d'une population d'embryons. / In addition to the Solar System and its planets, we now have a database of nearly 1000 planets that emphasize the huge diversity of planets and systems that can be formed. This diversity is a challenge for planetary formation models. Type I migration is one of the mechanisms possible to explain this diversity. Depending on disc properties, planets can migrate inward or outward with respect to their host star. The huge parameter space of protoplanetary disc models can form a huge diversity of planetary systems, in agreement with the diversity observed in the nonetheless small sample accessible to us. Thanks to numerical simulations, I showed that within the same disc, it is possible to form super-Earths or giant planet cores, depending on the migration history of an initial population of embryos.

Neste trabalho é apresentado um estudo observacional de discos de acresção em Variáveis Cataclísmicas (VCs). São analisadas medidas espectrofotométricas com resolução temporal dos perfis de linhas de emissão. A emissividade em linhas dos sistemas é mapeada utilizando a técnica de tomografia Doppler. Os parâmetros básicos das binárias, tais como período orbital, massas, inclinação orbital, são determinados quando necessário. Um código foi desenvolvido para simular a variabilidade das linhas de emissão em sistemas binários, além da presença de vento. O código foi utilizado para quantificar os parâmetros necessários para um estudo adequado de tomografia do flickering, tais como número de espectros, relação sinal-ruído destes, e frequência e amplitude do flickering em questão. Três sistemas são abordados: V3885 Sgr, RR Pic e V841 Oph. A variabilidade intrínseca de V3885 Sgr é mapeada através da técnica de tomografia do flickering. O flickering foi simulado e verificou-se que a fonte principal de flickering observada em V3885 Sgr não poderia se originar em um disco de acresção Kepleriano, mas sim na face iluminada da estrela secundária. Uma interpretação proposta para este fenômeno seria de um cenário onde o flickering no contínuo UV originado nas regiões centrais do disco ou na mancha quente é reprocessado na face iluminada da secundária. Obtivemos a primeira confirmação, para uma Variável Cataclísmica de curto período (RR Pic), de uma secundária com relação massa/raio distante da sequência principal. No caso de V841 Oph determinamos o período orbital e obtivemos uma razão de massas um pouco inferior a 1. Verificamos a existência de uma região de emissão mais intensa localizada no quadrante oposto ao esperado para a mancha quente, sendo esta região particularmente brilhante em HeI. O disco de acresção de V841 Oph foi verificado como sendo de baixa emissividade em linhas. / An observational study of accretion disks in Cataclysmic Variables (CVs) is presented in this work. Time-resolved spectrophotometric data of the emission line profiles are analyzed. The line emissivity of the systems is mapped using the Doppler tomography technique. The basic orbital parameters of the systems, like the orbital period, mass, orbital inclination, are determined when needed. A code was developed to simulate the emission line profile variability in binary systems, also including the presence of a wind. Such a code was used to quantify the parameters involved in a flickering tomography study, like the number of spectra, signal-to-noise ratio, frequency and amplitude of the flickering. Three systems are analyzed: V3885 Sgr, RR Pic and V841 Oph. The intrinsic variability in V3885 Sgr is mapped using the flickering tomography technique. The flickering was simulated and we have verified that the main flickering source in V3885 Sgr could not be located on the Keplerian accretion disk. The inner face of the secondary star is proposed instead. One interpretation of this phenomenon is a scenery where flickering in the UV continuum from the inner parts of the accretion disk is reprocessed at the illuminated face of the secondary star. The first confirmation of a secondary star with a mass-radius relation far from the main sequence values was obtained for a CV with a short period (RR Pic). In the case of V841 Oph we determined the orbital period and obtained a mass-ratio slightly below 1. We verified the presence of a region of enhanced emission in the quadrant opposite to the one expected for the hot spot. The emission of this region is particularly enhanced in HeI. The V841 Oph accretion disk was verified as being of low emissivity in lines.

[Special characters cannot be displayed. Please see the pdf version of the Abstract for an accurate reproduction.] We studied the circumstellar discs, the initial mass function (IMF), mass distribution, binarity and the fundamental properties of the [special character] 9 Myr-old pre-main sequence (PMS) [special character] Chamaeleontis cluster. Using JHKL colour-colour and colour-excess diagrams, we found the circumstellar disc fraction to be [special character] 0.60 among the late-type members. Four stars with [special character] (K - L) > 0.4 were identified as experiencing ongoing accretion which was later confirmed by high-resolution spectroscopic study. Quantitative analysis of the H[special character] profiles found accretion in these four stars at rates comparable to that of two members of the similarly-aged TW Hydrae Association (TWA); rates 1 - 3 orders of magnitude lower than in younger classical T Tauri stars. Together these results suggest that, while the mass accretion rate decreases with age, PMS stars can retain their inner discs for [special character] 10 Myr. An optical photometric survey spanning 1.3 ?? 1.3 pc added two low-mass stars to the cluster inventory. Together with other recent surveys the population is likely to be significantly complete for primaries with masses M > 0.15M[special character]. The cluster now consists of 18 primaries and 9 confirmed and candidate secondaries, with [special character] 2-4 times higher multiplicity than seen in field dwarfs. The cluster IMF is consistent with that of rich young clusters and field stars. By extending the IMF to lower masses, we predict 20-29 low-mass stars and brown dwarfs may remain undiscovered. From study of the cluster???s spatial and mass distribution, we find the [special character] Cha cluster has significant mass segregation, with > 50 per cent of the stellar mass residing within the central 0.17 pc. Lastly we classified members of the cluster with low-resolution spectra, providing information about the fundamental properties of the PMS stars by comparison to standard dwarfs. Broadband VRI colours and pseudocontinuum indices derived for the cluster stars are indistinguishable from dwarfs at visual and red wavelengths. This suggests the temperature sequence for the PMS [special character] Cha cluster is similar to that of the dwarf sequence. Narrow-band spectral indices for the [special character] Cha cluster possibly indicate higher metallicity and strongly indicate lower surface gravity than the dwarf indices.

Mes travaux de recherche portent sur l'étude du rayonnement (surtouts rayons X durs) provenant des trous noirs accrétant (dans les noyaux actifs de galaxies et les binaires X). L'objectif est d'en extraire des informations sur les conditions physique régnant dans l'environnement immédiat de ces objets. Les principales question auxquelles je tente de répondre sont les suivantes: Quelle est la structure et la géométrie de la matière accrétée au voisinage du trou noir ? Comment celle -ci évolue-t-elle avec le taux d'accrétion de masse ? Quel est la relation entre les processus d'accrétion et la formation de jets souvent observés dans ces systèmes ? Mon approche est fondée sur une comparaison précise entre les observations et les prédictions des divers modèles. Je présente les efforts poursuivis depuis près de dix ans afin de développer des outils de simulation numérique pour modéliser le transfert de rayonnement dans les plasma chauds des sources compactes X. Je montre comment ces outils ont été utilisés pour modéliser le continuum haute énergie et la variabilité des trous noirs accrétants et pour contraindre la structure du flot d'accrétion. Je présente également des résultats reposant sur l'analyse et l'interprétation d'observations menées avec des télescopes spatiaux tels que XMM-Newton et INTEGRAL ainsi que sur des d'observations simultanées à plusieurs longueurs d'ondes allant de la radio aux rayons X durs.

The current paradigm in planet formation theory is developed around a hierarquical growth of solid bodies, from interstellar dust grains to rocky planetary cores. A particularly difficult phase in the process is the growth from meter-size boulders to planetary embryos of the size of our Moon or Mars. Objects of this size are expected to drift extremely rapid in a protoplanetary disk, so that they would generally fall into the central star well before larger bodies can form. In this thesis, we used numerical simulations to find a physical mechanism that may retain solids in some parts of protoplanetary disks long enough to allow for the formation of planetary embryos. We found that such accumulation can happen at the borders of so-called dead zones. These dead zones would be regions where the coupling to the ambient magnetic field is weaker and the turbulence is less strong, or maybe even absent in some cases. We show by hydrodynamical simulations that material accumulating between the turbulent active and dead regions would be trapped into vortices to effectively form planetary embryos of Moon to Mars mass. We also show that in disks that already formed a giant planet, solid matter accumulates on the edges of the gap the planet carves, as well as at the stable Lagrangian points. The concentration is strong enough for the solids to clump together and form smaller, rocky planets like Earth. Outside our solar system, some gas giant planets have been detected in the habitable zone of their stars. Their wakes may harbour rocky, Earth-size worlds.

In this thesis, X-ray spectral and pulse timing analysis of the high mass X-ray binary pulsar 4U 1907+09, based on the observations with Rossi X-ray Timing Explorer (RXTE) and International Gamma-Ray Astrophysics Laboratory (INTEGRAL), are presented. INTEGRAL (October 2005 - November 2007) and RXTE (June 2007 - December 2008) observations confirm that the luminosity of the source is highly variable such that, flaring and dipping activities are observed. The results of time-averaged energy spectra of RXTE and INTEGRAL observations are consistent with the previous studies. Orbital phase resolved spectroscopy with RXTE data, reveals that the Hydrogen column density varies through the orbit reaching to its maximum value just after periastron. This variation approves that the location of the absorbing material is the accretion flow. A slight spectral softening with increasing luminosity is aslo observed. 4U 1907+09 had been steadily spinning down for more than ~15 years with a rate of -3.54x10-14 Hz s-1. RXTE observations of the source in 2001 showed a ~60% decrease in the spin-down rate and INTEGRAL observations in 2003 showed a reversal to spin-up. The timing analysis presented in this thesis reveals a new spin-down episode with a rate of -3.59x10-14 Hz s-1, which is close to the previous steady spin-down rate. This result implies that a recent torque reversal before June 2007 has taken place. The reversal is a rare event for 4U 1907+09 and it indicates the variations in the mass accretion rate and/or geometry. Using RXTE observations, 24 new pulse periods are measured to demonstrate the period evolution. Energy resolved pulse profiles confirm that the profile has a double peak sinusoidal shape at energies below 20 keV, whereas the leading peak significantly loses its intensity above 20 keV. This energy dependence indicates that the physical circumstances of the two polar caps are different.