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
A dense region of a gaseous and dusty cloud collapses to form a protostar surrounded by a disk and an envelope. This thesis uses both observations and models to study physical and chemical... Show moreA dense region of a gaseous and dusty cloud collapses to form a protostar surrounded by a disk and an envelope. This thesis uses both observations and models to study physical and chemical conditions of these protostellar systems which are likely where planets start to form. From the observational side, ALMA is used to quantify abundance ratios of complex organic molecules (COMs) in the gas around young protostars. These ratios are found to be remarkably constant for various nitrogen-bearing COMs which points to formation of these molecules under similar conditions, likely in ices of the prestellar phase. Moreover, observations of JWST are used to tentatively detect molecules such as methyl cyanide and ethyl cyanide in interstellar ices for the first time. In addition, high angular resolution ALMA observations of a protostellar system are analyzed to report the first detection of a disk wind candidate in methanol and hydrogen cyanide. From the modeling side, radiative transfer models are used to investigate how physical conditions such as source structure can change the molecular emission and molecular abundances. These models show that disk and optically thick dust can decrease the emission from COMs and change the correlations among their column densities. 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
This thesis discusses the physical and chemical processes than influence the composition of forming planets. The focus is on the effect of these processes on the abundance and distribution of... Show moreThis thesis discusses the physical and chemical processes than influence the composition of forming planets. The focus is on the effect of these processes on the abundance and distribution of moleculus in the birth places of planets, proto-planetary disks. The thesis further discusses how current and future observations can be used to quantify the effects of these processes. A good grasp of these processes will enable researchers to link the composition of (exo)planets to their formation origin. Specifically this thesis studies the the most abundant carbon and oxygen carrying molecules, CO, CO2 and H2O. Chemical modelling of CO indicates that conversion of CO into other molecules needs to be fast to explain the current observations. Study of the transport and distribution of CO2 indicate that the measured the CO2 abundance in the surface layers of disks is not bulk CO2 abundance. The power of spectroscopic CO observations in the infrared to find physical structures in disks, possibly created by planets is also discussed. Finally, a combination of infrared observations is used to show that the closest proto-planetary disk is poor in molecules that contain carbon and oxygen, indicating that a process is removing these molecules from the gas phase. Show less
Star and planet formation is intimately linked through the protostellar disk. Understanding the formation and evolution of this disk is crucial to determine the physical and chemical processes that... Show moreStar and planet formation is intimately linked through the protostellar disk. Understanding the formation and evolution of this disk is crucial to determine the physical and chemical processes that occur from the formation of dense molecular clouds to the emergence of life. Yet, the formation and early evolution of the protostellar disk are still not well explored. This thesis presents both observational and theoretical aspects of the early stages of disk formation and evolution. Hydrodynamical simulations of disk formation are coupled with multi-frequency continuum radiative transfer to determine the dust temperature. The detailed dust temperature structure is crucial for the construction of chemical structure. Observational predictions are simulated through molecular line radiative transfer methods to be compared with spectrally and spatially resolved data. By comparing these predictions with observational data, it is possible to link the disk formation process with planet formation Show less
