High-angular-resolution observations of the circumstellar material have uncovered numerous and very diverse substructures in protoplanetary discs, raising the question of whether they are caused by... Show moreHigh-angular-resolution observations of the circumstellar material have uncovered numerous and very diverse substructures in protoplanetary discs, raising the question of whether they are caused by forming planets or other mechanisms. This dissertation focuses on interpreting gas substructures in discs in the context of disc winds and planet-disc interactions. A special focus is put on transition discs, which show dust (and gas) depleted inner regions and represent ideal laboratories to observe planet formation in action and test disc evolution models. Radiative transfer and hydrodynamical models are combined to investigate photoevaporative winds acting in discs in which volatile carbon is reduced. Compared to solar metallicity discs, photoevaporative winds are stronger in such carbon-depleted discs, resulting in higher mass-loss rates and profiles that extend to larger radii. This may explain more of the observed transition disc population. Furthermore, a large number of transition discs are analysed through CO ALMA observations in terms of substructures in the kinematics and brightness temperatures. In particular, two sources, CQ Tau and HD 100546, are studied in detail and the analysis reveals prominent spiral features in both discs. Together with other substructures, these point towards ongoing planet formation. Show less
Circumstellar discs are the reservoirs of gas and dust that surround young stars and have the potential to become planetary systems. Their evolution will determine the time and material available... Show moreCircumstellar discs are the reservoirs of gas and dust that surround young stars and have the potential to become planetary systems. Their evolution will determine the time and material available to form planets. Studying the evolution of circumstellar discs can then help us understand planet formation and the diversity of observed planetary systems. These discs develop almost immediately after star formation, as a direct consequence of the collapse of a molecular cloud and angular momentum conservation. Their surroundings are rich in gas and neighbouring stars, which can be hostile to the discs and affect their evolution in different ways: dynamical encounters with nearby stars can truncate the discs; stellar winds and supernovae explosions can truncate, tilt, or completely destroy the discs; and the presence of bright, massive stars in the vicinity of circumstellar discs can heat their surface enough to evaporate mass from them. This process, known as external photoevaporation, is arguably one of the most important environmental mechanisms in depleting mass from young circumstellar discs. The work performed for this thesis consisted of simulating the early evolution of circumstellar discs in star clusters and the effects of the environment, in particular, truncations due to close encounters and photoevaporation. The results show that photoevaporation is extremely efficient in removing mass from the discs, greatly limiting the amount of material and time available to form planets. Show less
The study of exoplanets and the protoplanetary discs in which they form is a very challenging task. In this thesis we present several studies in which we investigate the potential of imaging... Show moreThe study of exoplanets and the protoplanetary discs in which they form is a very challenging task. In this thesis we present several studies in which we investigate the potential of imaging polarimetry at visible and near-infrared wavelengths to reveal the characteristics of these objects and overcome the scientific and technical challenges involved. Show less
The planets, comets, asteroids... all objects in the Solar system have become from a single disc of matter at the time Sun was a young star. In the recent years it has become possible to take... Show moreThe planets, comets, asteroids... all objects in the Solar system have become from a single disc of matter at the time Sun was a young star. In the recent years it has become possible to take images of such discs elsewhere in our Galaxy, but it soon became clear that each different 'camera' we use tells a different story about the disc. In this thesis, the state-of-the-art telescopes around the globe are used to image the distribution of matter in such discs around young distant stars. We combine different pieces of information together, in a single model, and test this model against images that probe the basic disc properties: its size, mass and shape. These hi-tech snapshots of the childhood of a planetary system show that a disc may extend much further and not be as smooth as previously thought. This thesis concludes that the structure of the disc as a whole cannot be constrained without the interferometric images, and demonstrates that it is essential to combine them with the existing techniques and theory. Show less
