Molecular Footprints in the Deaths and Births of Stars: Observing Carbon-rich Chemistry from Evolved Stars to Prestellar Clouds

Author: ORCID icon
Siebert, Mark, Astronomy - Graduate School of Arts and Sciences, University of Virginia
Remijan, Anthony, UVA/NRAO

Tracing the production and evolution of carbon compounds in astronomical sources is a key piece of understanding the cosmic origins of organic material in the solar system. In the Milky Way, carbon is recycled in the form of dust and aromatics through the mass-loss of evolved stars. Then, after being subject to the energetic, chemically active conditions of the interstellar medium and star formation, this material is incorporated into planetary systems. This progression is crucial to astrobiology; however, many of the processes which shape the composition of interstellar and circumstellar carbon are still largely unconstrained. In this thesis, I present several radio spectroscopic studies of molecular carbon in both dying stars and cold prestellar clouds. The aim of these works is to better characterize the dominant chemical pathways leading to large carbonaceous species, and understand how this chemistry is linked to the physical/dynamical properties of a particular source.
In Chapters 2–5, I highlight three AGB-related stellar outflows as key case studies for understanding C-rich recycling in complex circumstellar morphologies: CW Leo (IRC+10216), V Hya, and V510 Pup. Though these sources exist at different stages of evolution, they are linked by the presence of a binary companion dynamically perturbing their circumstellar structure. These case studies will detail the rapid growth of hydride species, binary-induced photochemistry, and the unique molecular distributions present in circumbinary disks and jets. In Chapter 6, I investigate the production of large carbon chains in the dark molecular cloud TMC-1, and present the discovery of a new symmetric top molecule CH3C7N through spectral stacking methods. Through this analysis, I show that nitrogen-terminated chains exhibit a distinct chemistry from their pure hydrocarbon counterparts.

PHD (Doctor of Philosophy)
Astrochemistry, Stellar evolution, Radio astronomy, AGB stars
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