Tracing the Earliest Stages of Planet Formation through Modelling and Sub-mm Observations

Abstract

This thesis explores the utility of molecular line emission as a tool to unravel the physical structures and processes involved in planet formation. Observations of molecular ions, HCO+ and DCO+, in the disk of DM Tauri allow for a study of the ionization structure. These constraints are an essential ingredient in modelling the physical and chemical evolution of a disk which directly impact the efficiency of planet formation. We also present the first spatially resolved direct measurement of turbulence in a protoplanetary disk using CO, CN and CS molecular line emission. Such a measurement is vital in identifying the physical mechanisms driving turbulence. In addition, we perform a thorough analysis of all uncertainties involved when determining turbulent velocities in disks and demonstrate that all measurements of turbulence will be ultimately limited by the precision to which the gas temperature can be derived. Finally, the CS emission profile from TW Hydrae displays a dip-like feature coincident with features observed in scattered light observations of the disk, suggesting a common origin. Extensive modelling demonstrates that this may be the first detection of a surface density perturbation through molecular line emission, potentially the manifestation of an embedded protoplanet or a strong magneto-rotational instability.