A large diversity of exoplanetary systems has been found, but it is still unclear what drives this diversity. Planets are formed in disks around young stars, but the sensitivity and resolution of... Show moreA large diversity of exoplanetary systems has been found, but it is still unclear what drives this diversity. Planets are formed in disks around young stars, but the sensitivity and resolution of pre-ALMA data have allowed only a handful of disks to be characterized. ALMA has opened up the possibility to survey hundreds of disks in both the gas and dust, and to also spatially resolve them. The most recent observations of protoplanetary disks in the (sub-)mm emission and in optical/near-infrared scattered light have revealed complex structures such as spirals, rings, gaps and vortices. Planets are often invoked as an explanation, but their number and location are degenerate, and the same system can be often explained by more than one scenario. In this thesis, the origin of these gas and dust structures both through dust observations and through chemical modelling of the gas emission is studied, and the link between the structures observed in the different tracers is investigated.These studies are critical to understand if substructures in disks are the signpost of ongoing planet formation and will ultimately also tell whether and how the variety of structures observed is linked to the diversity in the exoplanetary systems’ properties. Show less
Keppler, M.; Benisty, M.; Müller, A.; Henning, T.; Boekel, R. van; Cantalloube, F.; ... ; Weber, L. 2018
Aims. To understand planet formation it is necessary to study the birth environment of planetary systems. Resolved imaging of young planet forming disks allows us to study this environment in great... Show moreAims. To understand planet formation it is necessary to study the birth environment of planetary systems. Resolved imaging of young planet forming disks allows us to study this environment in great detail and find signs of planet-disk interaction and disk evolution. In the present study we aim to investigate the circumstellar environment of the spectroscopic binary T Tauri star CS Cha. From unresolved mid-to far-infrared photometry it is predicted that CS Cha hosts a disk with a large cavity. In addition, spectral energy distribution modeling suggests significant dust settling, pointing toward an evolved disk that may show signs of ongoing or completed planet formation.Methods. We observed CS Cha with the high contrast imager SPHERE at the ESO Very Large Telescope (VLT) in polarimetric differential imaging mode to resolve the circumbinary disk in near-infrared scattered light. These observations were followed up by VLT/NACO L-band observations and complemented by archival VLT/NACO K-band and Hubble Space Telescope WFPC2 I-band data.Results. We resolve the compact circumbinary disk around CS Cha for the first time in scattered light. We find a smooth, low inclination disk with an outer radius of ~55 au (at 165 pc). We do not detect the inner cavity but find an upper limit for the cavity size of ~15 au. Furthermore, we find a faint comoving companion with a projected separation of 210 au from the central binary outside of the circumbinary disk. The companion is detected in polarized light and shows an extreme degree of polarization (13.7 ± 0.4% in the J band). The J- and H-band magnitudes of the companion are compatible with masses of a few MJup. However, K-, L-, and I-band data draw this conclusion into question. We explore with radiative transfer modeling whether an unresolved circum-companion disk can be responsible for the high polarization and complex photometry. We find that the set of observations is best explained by a heavily extincted low-mass (~20 MJup) brown dwarf or high-mass planet with an unresolved disk and dust envelope. Show less
The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the... Show moreThe Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that a breakthrough in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to 100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the "Hill Sphere" of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. Our science working group has investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. In this contribution we outline the key science drivers of PFI and discuss the requirements that will guide the technology choices, the site selection, and potential science/technology tradeoffs. Show less
Context. Transition disks are protoplanetary disks with inner depleted dust cavities that are excellent candidates for investigating the dust evolution when there is a pressure bump. A pressure... Show moreContext. Transition disks are protoplanetary disks with inner depleted dust cavities that are excellent candidates for investigating the dust evolution when there is a pressure bump. A pressure bump at the outer edge of the cavity allows dust grains from the outer regions to stop their rapid inward migration towards the star and to efficiently grow to millimetre sizes. Dynamical interactions with planet(s) have been one of the most exciting theories to explain the clearing of the inner disk. Aims. We look for evidence of millimetre dust particles in transition disks by measuring their spectral index αmm with new and available photometric data. We investigate the influence of the size of the dust depleted cavity on the disk integrated millimetre spectral index. Methods. We present the 3-mm (100 GHz) photometric observations carried out with the Plateau de Bure Interferometer of four transition disks: LkHα 330, UX Tau A, LRLL 31, and LRLL 67. We used the available values of their fluxes at 345 GHz to calculate their spectral index, as well as the spectral index for a sample of twenty transition disks. We compared the observations with two kinds of models. In the first set of models, we considered coagulation and fragmentation of dust in a disk in which a cavity is formed by a massive planet located at different positions. The second set of models assumes disks with truncated inner parts at different radii and with power-law dust-size distributions, where the maximum size of grains is calculated considering turbulence as the source of destructive collisions. Results. We show that the integrated spectral index is higher for transition disks (TD) than for regular protoplanetary disks (PD) with mean values of = 2.70 ± 0.13 and = 2.20 ± 0.07 respectively. For transition disks, the probability that the measured spectral index is positively correlated with the cavity radius is 95%. High angular resolution imaging of transition disks is needed to distinguish between the dust trapping scenario and the truncated disk case. Show less
