Tracing Organic Complexity During Star and Planet Formation
Bergner, Jennifer Beth
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CitationBergner, Jennifer Beth. 2019. Tracing Organic Complexity During Star and Planet Formation. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractIn this thesis, we use laboratory experiments and millimeter telescope observations to explore the origins of organic complexity in star- and planet-forming regions.
The laboratory experiments presented here test new pathways to chemical complexity in very cold interstellar environments. An outstanding issue in astrochemical models is that existing frameworks cannot explain the detection of complex (6+ atom) organic molecules, or COMs, in cold (∼10K) environments. We explore two new ice-phase channels, ion formation chemistry and oxygen atom chemistry, as possible avenues of COM formation under these conditions. For each of these test systems, we use kinetic modeling to constrain reaction energy barriers, and infer reaction mechanisms and other relevant microphysical parameters. While ion formation chemistry may be limited in very cold environments due to moderate diffusion barriers, oxygen atom chemistry represents a promising pathway to chemical complexity at low temperatures.
Using millimeter telescope observations, we study the organic chemistry along the evolutionary sequence of low-mass star formation. We present a survey of line emission an unbiased sample of embedded protostars, enabling us to derive statistics on COM detection frequencies and abundances for typical protostellar envelopes. On smaller scales, we survey the COM chemistry of five protostellar disk candidates and find that three sources host warm, COM-rich hot corinos, suggesting a physical and/or evolutionary association between these structures. In more evolved, planet-forming disks we study the emission of the complex nitriles CH3CN and HC3N, expanding our understanding of COM chemistry at comet-forming disk radii. We also explore C2H, HCN, and C18O emission in protoplanetary disks, allowing us to probe the relationship between carbon, nitrogen, and oxygen chemistry in disks. By constraining the abundances and distributions of simple and complex organic molecules at different evolutionary stages, we are assembling a view of how the organic chemistry evolves during star and planet formation.
We have explored both the mechanisms and the outcomes of organic chemistry in the progenitors of planetary systems, bringing us closer to understanding how prebiotically important material is delivered to nascent planets.
Citable link to this pagehttp://nrs.harvard.edu/urn-3:HUL.InstRepos:42029574
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