This thesis focusses on the temperature structure in protoplanetary disks. The relation between structures seen in the dust and gas-phase molecules is investigated. This is crucial to understand... Show moreThis thesis focusses on the temperature structure in protoplanetary disks. The relation between structures seen in the dust and gas-phase molecules is investigated. This is crucial to understand the chemical composition of the planet forming material as well as to quantify the amount of gas present in the disk, a crucial parameter to determine if planets are likely present in the disk. One of the important regions in the disk is the water snowline, the midplane location where water freezes-out onto the dust grains. In this thesis, chemical modelling is used to infer the snowline location in a hot disk. This result is confirmed in the next chapter by 2D imaging of the water snow surface, the 2D equivalent of the water snowline. Additionally, the temperature structure across transition disk cavities is investigated to determine the mass of the planets that may be carving that cavity. Finally, the relation between the structures traced in the gas by different molecules and the dust is investigated to show that the chemical composition at the location of the dust rings and dust trap in the HD 100546 and OPH-IRS 48 disks, respectively, are different than in the other disk regions. Show less
Detecting planets during their formation stages is crucial for understanding the history and diversity of fully developed planetary systems like our own. However, observing young planets directly... Show moreDetecting planets during their formation stages is crucial for understanding the history and diversity of fully developed planetary systems like our own. However, observing young planets directly is challenging because they are often deeply embedded within their host protoplanetary discs, rich in gas and dust. To overcome this limitation, this thesis introduces a novel methodology for identifying coherent kinematic perturbations in discs induced by giant planets orbiting stars with a mass similar to that of the Sun. This approach not only allows us to investigate the presence of planets but also to determine their most likely radial and azimuthal positions in a statistically robust manner. Moreover, it offers the additional benefit of enabling a three-dimensional reconstruction of the physical and dynamical structure of these planet-forming environments by simultaneously modelling the emission of multiple molecular tracers.The methodology is applied to various protoplanetary discs observed using the world-class interferometer ALMA, revealing a wide variety of kinematic and temperature features. These features include large-scale substructures with spiral and ring-like morphologies, as well as localised perturbations, some of which span coherently across the vertical extent of the disc indicating meridional circulation of material. Among the eight discs analysed, five exhibit signatures in the outer regions that could potentially be associated with massive embedded planets, suggesting that the interaction between discs and wide-orbit giant planets may represent a common early mechanism with a fundamental role in shaping the evolution of discs and, as a result, in the assembly and composition of planetary systems. Show less
This thesis focuses on protoplanetary disks: flattened structures of gas and dust around young stars in which planets are expected to form and grow. Physical-chemical models that compute the... Show moreThis thesis focuses on protoplanetary disks: flattened structures of gas and dust around young stars in which planets are expected to form and grow. Physical-chemical models that compute the thermal structure and chemical composition of protoplanetary disks are compared to observations to increase our understanding of the processes that shape these disks.Chapters two and three investigate the sizes of protoplanetary disks in the context of evolution of the dust. A gas disk that is observed to be four times more extended than the dust disk is found to be a clear indication that the dust has drifted inward. Detailed modeling reveals that five out of a sample of 10 disks in the Lupus star-forming region show evidence for dust evolution. Chapter four shows that observed gas outer radii are consistent with disks evolving viscously, assuming disks start out small and evolve slowly. Chapter five reveals that the chemical conversion of CO into more complex species cannot by itself explain the low observed CO isotopolog line fluxes. Finally, Chapter six uses non-detections of the HD emission line to put an upper limit on the total mass of disks and rules out that they are currently gravitationally unstable. Show less
