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Presenter: Allison Bair, Research Associate at Lowell Observatory, Flagstaff, AZ
Education: B.A., Geoscience, Univeristy of Iowa, 2000; M.S. Quaternary Sciences, Northern Arizona University, 2004

Talk Title: "The Chemical and Physical Properties of Comets: Results from 50 Years of Narrowband Measurements at Lowell Observatory"

Investigations of the chemical and physical properties of comets reveal unique clues to conditions in the early solar nebula and the solar system's formation processes. A major goal of our research is to disentangle the comet properties related to formation conditions from those that arise from evolutionary processes due to thermal heating – a result of how long these objects have spent in the inner solar system. An additional objective is to establish individual as well as group properties of comets, and to quantify the degree to which an individual comet may vary from the ensemble. To address these goals, we utilize statistical analyses of the chemical, physical, and orbital properties of a large number of comets. We have sought to determine the ranges in composition, intrinsic activity levels, and rate of responses to changing solar heating displayed by these small icy bodies. 

In this presentation, after first giving an overview of comets and cometary research, I will talk about narrowband photometric measurements of comets obtained during the past half-century. The Lowell Observatory photometry database contains nearly 5,000 measurement sets of 235 comets. We have multiple apparitions of 37 periodic comets, as well as monthly observations for a significant number of individual comets that range as long as a year or more. With this information, we are not only able to derive their chemical compositions and bulk physical characteristics, but also to track their behavior as they approach and recede from the Sun. Our preliminary results have revealed six chemical compositional classes, most of which are clearly associated with the primordial conditions when and where the comets formed. We have investigated additional properties for correlations with orbital parameters, including production rates with heliocentric distance, seasonal behaviors, long-term trends in activity, bulk water production, fractional active surface areas, and dust-to-gas ratios, with most comets showing trends due to evolutionary (i.e. erosional) processes.