RUI: High Resolution Infrared Spectroscopic Observations and Characterization of Ammonia in Comets

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Abstract - Karen Magee-Sauer The prime objective of the research to be carried out is to make measurements of the ammonia (NH3) abundance in several comets and to measure the spatial profile and other characteristics of the emission. Models of solar nebula chemistry predict that the dominant nitrogen gas in the solar nebula was Nitrogen (N2) while the dominant nitrogen gas in the sub-nebulae of the giant planets was ammonia (NH3) (Fegley and Prinn, 1989). The ratios N2/NH3 and NH3/H20 enable on e to test solar nebula models and are important diagnostics of the origins of cometary ices (Lunine 1989, Fegley and Prinn 1989, Womack et al. 1992). Ammonia (NH3) had long been believed to be a significant reservoir for volatile nitrogen in comets, but until recently its presence had not been directly observed. The advancement of infrared detector technology has made it possible to directly detect NH3 in comets via its rotational vibrational transitions in the 3.0 micron wavelength region. The observations will consist of detecting the rotational- vibrational transition in the 3 micron wavelength region of the nu-1 vibrational band of NH3. The g-factors (fluorescence efficiency factors) of the Q, R-, and P- branches within this band are not available. In order to relate the observed intensity of its spectral lines to a production rate of ammonia, these g-factors need to be known. Therefore, as part of my analysis for the relative abundance of NH3, I will calculate the relevant nu-1 g- factors using known laboratory band intensities and non-LTE rotational distributions appropriate for cometary conditions. The focus of this project is on observing the NH3 in comets, and the results of this research will provide important information on the NH3 abundance and nature of the emission. The results will be used to help answer the basic question of the origin of comets, study whether NH3 is a parent molecule present as a natal ice in comets, and by examining the spatial ch aracteristics associated with the emission, and determine whether some ammonia is produced from an extended source. Undergraduate students at Rowan College of New Jersey will assist in developing data reduction techniques and in analyzing the data.