A Study of Protoplanetary Disk Evolution in Infrared CO
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The inner radii (< 10 AU) of protoplanetary disks (PPDs) are the birthplaces of exoplanets. Understanding what happens at these planet-forming distances requires the knowledge of inner gaseous disk evolution. Carbon monoxide (12CO; hereafter CO) gas is known to be an effective tracer of excited molecular gas at small radii (0.01 AU – 10 AU). Therefore, in this work, the depletion of molecular gas is traced as the planet-forming regions of PPDs evolve and become gas-poor. To probe CO gas properties, a LTE (local thermal equilibrium) molecular excitation model is employed. Spectral emission of CO and H2 (molecular hydrogen) gas are compared to analyze gas properties in both gas-rich, full disks and gas-poor transition disks. This approach demonstrates a radial stratification of molecular gas: CO lines are increasingly narrower than H2 lines for disks with large inner gaps, or cavities, suggesting a recession of CO gas in the inner disk. In this thesis, I report results from an excitation analysis of CO spectra to identify how inner disk gas properties change as inner dust cavities form.