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
In this thesis we study the earliest stages of high-mass star formation. Class II methanol masers are only associated with massive star formation and are a unique probe of these environments.... Show moreIn this thesis we study the earliest stages of high-mass star formation. Class II methanol masers are only associated with massive star formation and are a unique probe of these environments. Through observations we have studied where and when the methanol maser emission occur in relation to the protostar. We have found that for a fair fraction of the sources the methanol masers appear on size scales of ca. 1000 AU, in the equatorial region of the massive protostar. It appears that infall, rather than rotation, is the dominant motion. We propose that the maser emission occur close to or in a shock interface, possibly related to the accretion flow of the more extended gas in the protostellar envelope onto an accretion disk. The morphology and kinematics of the thermal methanol gas support the hypothesis that the maser region is also the region where the methanol molecules are released from the icy mantles of the du st grains. We have also estimated the temperature and column density of the methanol gas in the outflows and find evidence for radiative excitation of the methanol gas at the location of the maser emission. Show less
Gold nanoparticles are spherical clusters of gold atoms, with diameters typically between 1 and 100 nanometers. The applications of these particles are rather diverse, from optical labels for... Show moreGold nanoparticles are spherical clusters of gold atoms, with diameters typically between 1 and 100 nanometers. The applications of these particles are rather diverse, from optical labels for biological experiments to data carrier for optical data storage. The goal of my project was to develop new methods to study the physical properties of single gold nanoparticles on ultra-short timescales. Exciation with a short laser pulse brings a nanoparticle out of equilibrium, which makes it vibrate with a period that depends on the particle diameter and the speed of sound in gold. The vibrational period of a gold nanoparticle with a diameter of 60 nanometer is 20 picoseconds. This acoustic vibration has been detected by us for the first time for single particles. The main advantage of single-particle studies over bulk detection of these particles lies in the fact that all particles in an ensemble vibrate at slightly different frequencies, which causes increased damping due to dephasing. The damping of the vibrations of single particles only depends on the elastic coupling between the particle and its environment, which offers the possibility of using these particles as mechanical nanosensors. Show less
