In this paper, we investigate the relation between disk mass and mass accretion rate to constrain the mechanism of angular momentum transport in protoplanetary disks. We find a correlation between dust disk mass and mass accretion rate in Chamaeleon I with a slope that is close to linear, similar to the one recently identified in Lupus. We investigate the effect of stellar mass and find that the intrinsic scatter around the best-fit M-dust-M star and M-acc-M star relations is uncorrelated. We simulate synthetic observations of an ensemble of evolving disks using a Monte Carlo approach and find that disks with a constant alpha viscosity can fit the observed relations between dust mass, mass accretion rate, and stellar mass but overpredict the strength of the correlation between disk mass and mass accretion rate when using standard initial conditions. We find two possible solutions. In the first one, the observed scatter in M-dust and M-acc is not primordial, but arises from additional physical processes or uncertainties in estimating the disk gas mass. Most likely grain growth and radial drift affect the observable dust mass, while variability on large timescales affects the mass accretion rates. In the second scenario, the observed scatter is primordial, but disks have not evolved substantially at the age of Lupus and Chamaeleon I owing to a low viscosity or a large initial disk radius. More accurate estimates of the disk mass and gas disk sizes in a large sample of protoplanetary disks, through either direct observations of the gas or spatially resolved multiwavelength observations of the dust with ALMA, are needed to discriminate between both scenarios or to constrain alternative angular momentum transport mechanisms such as MHD disk winds.

Les conditions thermodynamiques régnant au sein des planètes géantes telles que Jupiter, Saturne et bon nombre des exoplanètes découvertes quotidiennement, impliquent que les interactions entre particules – atomes, ions, électrons – sont prépondérantes dans les enveloppes planétaires, principalement composées d'hydrogène et d'hélium, et déterminent les propriétés mécaniques et thermiques de ces objets. La caractérisation de ces plasmas denses est donc cruciale pour comprendre la structure et l'évolution de ces planètes géantes. Les simulations ab initio, utilisant la théorie de la fonctionnelle de la densité, ont montré leurs performances pour la caractérisation des espèces pures dans leur phase plasma dense, en reproduisant correctement les résultats des expériences de chocs par laser haute-puissance. Néanmoins, des écarts importants perdurent entre modèles planétaires et observations. Ils sont attribués à la non-idéalité du mélange H-He et de possibles transitions de phase. Dans ce travail de thèse, ces méthodes numériques ab initio ont été appliquées au cas des mélanges H-He. L'étude thermodynamique a révélé des déviations sensibles par rapport aux prédictions obtenues pour des mélanges idéaux. Par ailleurs, les calculs des propriétés de transport (conductivité électrique, thermique, propriétés optiques...) ont montré une transition isolant-conducteur du mélange, notamment par l'ionisation de l'hydrogène. Celle-ci s'accompagne, dans un certain domaine de paramètres, d'une séparation de phase entre l'hydrogène conducteur et l'hélium neutre. Ces calculs ont également permis d'établir des diagnostics pour les expériences laser, afin de pouvoir corroborer cet ensemble de résultats et obtenir, à terme, une équation d'état fiable du mélange H-He, applicable aux planètes géantes. / The thermodynamical conditions inside the giant planets - like Jupiter, Saturn or many of the daily discovered exoplanets – are such that the interactions between particles – atoms, ions, electrons – are highly dominant in the physics of giant planets envelope s, mostly made of hydrogen and helium in a plasma phase. The heat and mechanical properties of these planets are mainly determined by these interactions. Thus, it is of crucial interest to study these dense plasmas to understand the structure and the evolution of the giant planets. The dense plasma phase of the pure compounds has been successfully characterized by ab initio simulations using density functional theory. For instance, they correctly reproduced the results obtained in high-power laser chock experiments. Nevertheless, large discrepancies remain between planetary models and observations. A proposed hypothesis is a strong influence of the H-He mixture non-ideality and possible phase separations. In this work, these ab initio numerical methods have been applied to the H-He mixtures. The thermodynamical study has shown sensitive deviations from ideal mixtures. The estimates of the transport properties (electrical and heat conductivities, optical properties...) indicate an insulator-conductor transition in the mixture, associated with hydrogen ionization. In some conditions, demixing of conducting hydrogen and neutral helium has also been observed. These computations have allowed us to determine pathways to verify our results through laser experiments. This is the first step in the establishment of a reliable equation of state of H-He mixtures, usable in giant planets modeling.

We present observations of the Herbig Ae star HD 169142 with the VLT/SPHERE instruments InfraRed Dual-band Imager and Spectrograph (IRDIS) (K1K2 and H2H3 bands) and the Integral Field Spectrograph (IFS) (Y, J and H bands). We detect several bright blobs at similar to 180 mas separation from the star, and a faint arc-like structure in the IFS data. Our reference differential imaging (RDI) data analysis also finds a bright ring at the same separation. We show, using a simulation based on polarized light data, that these blobs are actually part of the ring at 180 mas. These results demonstrate that the earlier detections of blobs in the H and K-S bands at these separations in Biller et al. as potential planet/substellar companions are actually tracing a bright ring with a Keplerian motion. Moreover, we detect in the images an additional bright structure at similar to 93 mas separation and position angle of 355 degrees, at a location very close to previous detections. It appears point-like in the YJ and K bands but is more extended in the H band. We also marginally detect an inner ring in the RDI data at similar to 100 mas. Follow-up observations are necessary to confirm the detection and the nature of this source and structure.

Dynamical mass estimates down to the planet-mass regime can help to understand planet formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of FW Tau C, a proposed similar to 10M(Jup) planet-mass companion at similar to 330 au from the host binary FW Tau AB. We spatially and spectrally resolve the accretion disk of FWTau C in (CO)-C-12 (2-1). By modeling the Keplerian rotation of gas, we derive a dynamical mass of similar to 0.1 M-circle dot. Therefore, FW Tau C is unlikely a planet, but rather a low-mass star with a highly inclined disk. This also suggests that FW Tau is a triple system consisting of three similar to 0.1. M-circle dot stars.

We present multi-wavelength radio observations obtained with the VLA of the protoplanetary disk surrounding the young brown dwarf 2MASS J04442713+2512164 (2M0444) in the Taurus star-forming region. 2M0444 is the brightest known brown dwarf disk at millimeter wavelengths, making this an ideal target to probe radio emission from a young brown dwarf. Thermal emission from dust in the disk is detected at 6.8 and 9.1 mm, whereas the 1.36 cm measured flux is dominated by ionized gas emission. We combine these data with previous observations at shorter sub-mm and mm wavelengths to test the predictions of dust evolution models in gas-rich disks after adapting their parameters to the case of 2M0444. These models show that the radial drift mechanism affecting solids in a gaseous environment has to be either completely made inefficient, or significantly slowed down by very strong gas pressure bumps in order to explain the presence of mm/cm-sized grains in the outer regions of the 2M0444 disk. We also discuss the possible mechanisms for the origin of the ionized gas emission detected at 1.36 cm. The inferred radio luminosity for this emission is in line with the relation between radio and bolometric luminosity valid for for more massive and luminous young stellar objects, and extrapolated down to the very low luminosity of the 2M0444 brown dwarf.

In 2014 February, the System for High contrast And coronography from R to K at VISual bands (SHARK-VIS) Forerunner, a high contrast experimental imager operating at visible wavelengths, was installed at the Large Binocular Telescope (LBT). Here we report on the first results obtained by recent on-sky tests. These results show the extremely good performance of the LBT Extreme Adaptive Optics (ExAO) system at visible wavelengths, both in terms of spatial resolution and contrast achieved. Similarly to what was done by Amara & Quanz (2012), we used the SHARK-VIS Forerunner data to quantitatively assess the contrast enhancement. This is done by injecting several different synthetic faint objects in the acquired data and applying the angular differential imaging (ADI) technique. A contrast of the order of 5 x 10(-5) is obtained at 630 nm for angular separations from the star larger than 100 mas. These results are discussed in light of the future development of SHARK-VIS and compared to those obtained by other high contrast imagers operating at similar wavelengths.

We present the Vortex Image Processing (VIP) library, a python package dedicated to astronomical high-contrast imaging. Our package relies on the extensive python stack of scientific libraries and aims to provide a flexible framework for high-contrast data and image processing. In this paper, we describe the capabilities of VIP related to processing image sequences acquired using the angular differential imaging (ADI) observing technique. VIP implements functionalities for building high-contrast data processing pipelines, encompassing pre- and post-processing algorithms, potential source. position and flux estimation, and sensitivity curve. generation. Among the reference point-spread. function subtraction techniques for ADI post-processing, VIP includes several flavors of principal component analysis (PCA) based algorithms, such as annular PCA and incremental PCA algorithms capable of processing big datacubes (of several gigabytes) on a computer with limited memory. Also, we present a novel ADI algorithm based on non-negative matrix factorization, which comes from the same family of low-rank matrix approximations as PCA and provides fairly similar results. We showcase the ADI capabilities of the VIP library using a deep sequence on HR 8799 taken with the LBTI/LMIRCam and its recently commissioned L-band vortex coronagraph. Using VIP, we investigated the presence of additional companions around HR 8799 and did not find any significant additional point source beyond the four known planets. VIP is available at http://github. com/vortex-exoplanet/VIP and is accompanied with Jupyter notebook tutorials illustrating the main functionalities of the library.

Many topics in planetary studies demand an estimate of the collision probability of two objects moving on nearly Keplerian orbits. In the classic works of Opik and Wetherill, the collision probability was derived by linearizing the motion near the collision points, and there is now a vast amount of literature using their method. We present here a simpler and more physically motivated derivation for non-tangential collisions in Keplerian orbits, as well as for tangential collisions that were not previously considered. Our formulas have the added advantage of being manifestly symmetric in the parameters of the two colliding bodies. In common with the Opik-Wetherill treatments, we linearize the motion of the bodies in the vicinity of the point of orbit intersection (or near the points of minimum distance between the two orbits) and assume a uniform distribution of impact parameter within the collision radius. We point out that the linear approximation leads to singular results for the case of tangential encounters. We regularize this singularity by use of a parabolic approximation of the motion in the vicinity of a tangential encounter.

We present evidence that the recently discovered, directly imaged planet HD 131399 Ab is a background star with nonzero proper motion. From new JHK1L' photometry and spectroscopy obtained with the Gemini Planet Imager, VLT/SPHERE, and Keck/NIRC2, and a reanalysis of the discovery data obtained with VLT/SPHERE, we derive colors, spectra, and astrometry for HD 131399 Ab. The broader wavelength coverage and higher data quality allow us to reinvestigate its status. Its near-infrared spectral energy distribution excludes spectral types later than L0 and is consistent with a K or M dwarf, which are the most likely candidates for a background object in this direction at the apparent magnitude observed. If it were a physically associated object, the projected velocity of HD 131399 Ab would exceed escape velocity given the mass and distance to HD 131399 A. We show that HD 131399 Ab is also not following the expected track for a stationary background star at infinite distance. Solving for the proper motion and parallax required to explain the relative motion of HD 131399 Ab, we find a proper motion of 12.3 mas yr(-1). When compared to predicted background objects drawn from a galactic model, we find this proper motion to be high but consistent with the top 4% fastest-moving background stars. From our analysis, we conclude that HD 131399 Ab is a background K or M dwarf.

Past ultraviolet and optical observations of stars hosting close-in Jupiter-mass planets have shown that some of these stars present an anomalously low chromospheric activity, significantly below the basal level. For the hot Jupiter planet host WASP-13, observations have shown that the apparent lack of activity is possibly caused by absorption from the intervening interstellar medium (ISM). Inspired by this result, we study the effect of ISM absorption on activity measurements (S and log R'(HK) indices) for main-sequence late-type stars. To this end, we employ synthetic stellar photospheric spectra combined with varying amounts of chromospheric emission and ISM absorption. We present the effect of ISM absorption on activity measurements by varying several instrumental (spectral resolution), stellar (projected rotational velocity, effective temperature, and chromospheric emission flux), and ISM parameters (relative velocity between stellar and ISM Ca II lines, broadening b-parameter, and Ca II column density). We find that for relative velocities between the stellar and ISM lines smaller than 30-40 km s(-1) and for ISM Ca II column densities log N-CaII greater than or similar to 12, the ISM absorption has a significant influence on activity measurements. Direct measurements and three dimensional maps of the Galactic ISM absorption indicate that an ISM Ca II column density of log N-CaII = 12 is typically reached by a distance of about 100 pc along most sight lines. In particular, for a Sun-like star lying at a distance greater than 100 pc, we expect a depression (bias) in the log R'(HK) value larger than 0.05-0.1 dex, about the same size as the typical measurement and calibration uncertainties on this parameter. This work shows that the bias introduced by ISM absorption must always be considered when measuring activity for stars lying beyond 100 pc. We also consider the effect of multiple ISM absorption components. We discuss the relevance of this result for exoplanet studies and revise the latest results on stellar activity versus planet surface gravity correlation. We finally describe methods with which it would be possible to account for ISM absorption in activity measurements and provide a code to roughly estimate the magnitude of the bias. Correcting for the ISM absorption bias may allow one to identify the origin of the anomaly in the activity measured for some planet-hosting stars.