High-Resolution Near-Infrared Observations Toward Protostellar Objects as Proxies for Solar System Chemical Evolution

Protostars and molecular clouds in the local solar neighborhood provide a unique opportunity to understand the isotopic evolution of our solar system. State-of-the-art high-resolution near-infrared spectroscopy may be used to obtain precise isotopologue ratios of CO to study both carbon and oxygen in evolving protostellar systems; these observations are comparable to meteoritic data illustrating isotopic anomalies in our solar system.;This thesis describes how the CO rovibrational absorption spectra obtained with the Cryogenic Infrared Echelle Spectrograph (CRIRES) on the Very Large Telescope in Chile, can be used to explore isotopic evolution in carbon and oxygen. The [16O]/[17,18O] and [12C]/[ 13C] abundance ratios enable the investigation of the oxygen isotope anomaly in solar system meteorites and the carbon isotope discrepancy between the solar system and local interstellar medium. The twelve lines-of-sight represent disks around young stellar objects, envelope material surrounding embedded protostars, and foreground molecular clouds; this diversity of objects facilitates the interpretation of isotopic results within an evolutionary context. Main results show (1) signatures of CO self-shielding in oxygen isotopes in at least two of the objects, and (2) indications of CO ice--gas partitioning by virtue of the general direct trend between the fraction of CO in the ice and the [12C16O]/[13C 16O] ratios observed in the gas.;The analyses presented here take advantage of the high resolving power of CRIRES (3.2 km s-1) which enabled modeling the line profiles directly for the optical depth and line width parameters, from which the column densities for each line were derived. This technique leads to much more precise molecular abundances than either emission lines or curve-of-growth modeling, both of which have been implemented in previous studies where either radio or lower-resolution lines necessitate these methods, requiring more extensive radiative transfer modeling. Results described in the following chapters reveal signatures of mass-independent fractionation in the oxygen isotopes for several objects, lending validity to the CO self-shielding hypothesis as an explanation for the oxygen isotope anomaly in the solar system. Also found is a correlation between the fraction of CO in the ice phase and the [12CO]/[ 13CO] abundance ratios in the gas for the objects in our sample, indicating that carbon isotope fractionation between the ice and gas phases should be considered in modeling carbon isotopic evolution in protostellar environments, with relevance to carbon evolution in our solar system.;The final chapter of this thesis describes preliminary results obtained by the RADLite ray-tracing code for modeling protostellar disks and envelopes. This code was implemented to generate CO spectra in axisymmetric protostellar environments in order to test the parameter space within which accurate CO isotopologue ratios may be derived by fitting a convolved Gaussian model to the CRIRES line profiles. So far, no systematic errors have been found within the confines of a simple inclined disk or spherical envelope. Effects of instrumental scattering have also been explored.;The overarching goal of this thesis is to show that high-resolution data open a window into detailed investigations of isotopic evolution in protostars, which is not possible using lower-resolution instrumentation. It is hoped that the techniques and results outlined here will lend support to future instrumentation with high-resolution near-infrared priorities, as well as new investigations of protostellar environments which may complement these isotopic studies and add to an expanding understanding of early solar system evolution.