Probing giant-planet forming zones around Solar-like stars with CO




Yu, Mo, Ph. D.

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Protoplanetary disks are dusty disks around young stars where planets are formed. The evolution and composition of protoplanetary disks determine the time, environments and materials available for planet formation. However fundamental properties of protoplanetary disks such as mass, composition, and the angular momentum transfer mechanism are poorly constrained by observations.

In this dissertation, we discuss the thermal and chemical evolution of protoplanetary disks around Solar-type stars, and evaluate methods to measure two key parameters - disk mass and turbulent velocity in the framework of an evolving disk system. We first build a chemical evolution model based on an MRI-active disk around a Solar-type star, and discuss the chemical depletion of CO due to the formation of complex organic molecules (Chapter 2). We then investigate the challenges one faces when measuring disk masses with CO due to the chemical depletion of CO and optical depth effects (Chapter 3). We propose strategies to correct for the CO depletion effect and constrain the disk mass within factor of a few accuracy. We also investigate the possibility of constraining turbulent velocities with CO line profiles in Chapter 4. Peak-to-trough ratios of CO rotational lines have been proposed as a robust probe for turbulent velocity. However we show that the peak-to-trough ratio could vary by 25% due uncertainties in effects of CO depletion. One would underestimate the degree of turbulence if the chemical depletion of CO is not properly accounted for.



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