The first half of this dissertation considers the evolution of the Universe at the scale of a single star, the Sun, and its solar system, using comets. I concentrate on characterizing the emission spectrum from the diatomic carbon C2 Swan bands. This fragment species is ubiquitous in comets. It is commonly used as a proxy to measure production rates of gas as well as a taxonomic classification tool. However, its parent species and the details of its emission are not well understood. A bimodal rotational temperature has been found in the Swan bands for comet 1P/Halley  (Lambert et. al. 1990). The following models have been proposed to explain this phenomenon: C2 inheriting excited states from the parent species (Jackson et. al. 1996), properties inherent to C2 through intercombinational/satellite transitions  (Lambert et. al. 1990), and multiple populations of C2 present in the photochemical environment (Lambert et. al. 1990). Leveraging a unique library of high resolution, high signal-to-noise optical spectra, collected at McDonald Observatory, I investigate the proposed mechanisms for this bimodality for comets 122P/de Vico, 153P/Ikeya-Zhang, and C/1995 O1 (Hale-Bopp). I find bimodal temperatures in all spectra studied and supersolar temperatures in C/1995 O1, which is incompatible with the models from the literature. I suggest the supersolar temperatures are a consequence of heating from the Solar wind. 

 

The second half of this dissertation considers cosmic fossils at the scale of the Galaxy. Photospheric abundances of stars are mostly conserved over their lifetimes, and therefore stars can act as chemical fossils for the Galaxy. I focus on the use of chemical tagging within the Milky Way. Chemical tagging of stars is one of the pillars of Galactic Archaeology, motivating numerous large scale surveys. It has dramatically reshaped our knowledge of the Galaxy over the last two decades. Chemical tagging relies upon stars which are born together, i.e. co-natal, sharing a common chemical composition. I find observational evidence for an untapped reservoir of co-natal, co-moving pairs of stars, through the application of chemical tagging. Co-natal stars provide an excellent laboratory for numerous areas of astronomy, from stellar physics, to survey calibration. A common application of chemical tagging is relating a wayward star to a possible birthplace. Hypervelocity stars (HVSs) are gravitationally unbound to the Milky Way, however the physical mechanisms that give rise to the large velocities of late-type HVSs are poorly understood. To solve this problem, I applied chemo-dynamic tagging to a sample of HVS candidates identified in Gaia data. Since these production mechanics are connected to specific locations or chemical environments within the Galactic neighborhood, chemical tagging can distinguish which production pathways could create these enigmatic fast stars.