Planets form in disks of gas and dust around young stars. Since the gas makes up 99 % of the disk mass, it is critical for our understanding of planet formation to gain direct information from the... Show morePlanets form in disks of gas and dust around young stars. Since the gas makes up 99 % of the disk mass, it is critical for our understanding of planet formation to gain direct information from the gas, independently of what can be learned from dust emission. In this thesis, calculations are presented of the chemistry and gas temperature in disks, and the resulting atomic and molecular emission lines are investigated. The main focus of the thesis is on the effects of dust settling on gas-phase emission lines of disks around T-Tauri and Herbig Ae stars. It is found that dust settling has little effect on the overall chemistry and molecular lines; the main effect is a decrease in the gas temperature, which is reflected in atomic fine-structure lines and especially in the [O I] lines. The chemistry, and especially the CO abundance and HCN/CN ratio, is affected more by the total gas mass than by the dust gas ratio in a disk. The models were also applied to the disk around HD 141569A, which is in a transitional stage between a gas-rich Herbig Ae disk and a debris disk. Using chemical models to fit the observed CO rotational lines it is concluded that gas and small dust particles have an approximately interstellar mass ratio, and that gas is still present in the inner hole in the dust distribution Show less
The formation of snow and ice has always intrigued humans and challenged them to study these phenomena. Every snowflake has its own unique history of formation, but no two are alike. Like snow... Show moreThe formation of snow and ice has always intrigued humans and challenged them to study these phenomena. Every snowflake has its own unique history of formation, but no two are alike. Like snow-crystals, interstellar ices consist predominantly of water (H2O), but also contain significant fractions of other molecules such as carbon monoxide (CO), carbon dioxide (CO2), and methanol (CH3OH), and traces of dinitrogen (N2) and ammonia (NH3). The presence, or absence, of a molecule in the ice strongly depends on the environmental conditions. Vice versa, these molecules have an influence on their environment as well. Hence, the chemical composition and the structure of interstellar ices are thought to contain valuable information about the past and the future of interstellar regions, and it is for this reason that interstellar ices are simulated and studied under laboratory conditions. The present thesis contains a study of laboratory analogs of interstellar ices and presents a newly developed apparatus that provides a novel laboratory route to investigate the properties of these ices in more detail than has previously been possible. Show less
