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M.C. Festou (SWRI), A.L. Cochran (Univ. of TX), J.-M. Zucconi (Obs. de Besancon, F), E.S. Barker, W.D. Cochran (Univ. of TX)
High resolution spectra of the B--X violet band of CN have been obtained at the McDonald Observatory in five comets. Resolutions range from 20 mÅ, to 80 m\AAGiven the very high S/N of these data, line widths can be measured with an accuracy significantly better than the theoretical resolution (to achieve this requires the assumption of the line shape and to compare a coma model to the data; direct inversion of the line profiles is impossible). The comparison of the line shapes and intensities of comets as different as comets Hale-Bopp (very gassy and observed over a wide range of heliocentric distances), Hyakutake (gassy and observed at very high spatial resolution) and periodic comets like 122P/de Vico (extremely low dust-to-gas ratio, observed at small heliocentric distance, comparison of coma and tail spectra), Tempel-Tuttle (low gas production) and GZ (low gas production, C2 and NH2-depleted) will allow us to address various questions such as the value of the velocity of the CN radicals and its relationship to the nature of its parent molecule(s), the effect of collisions with the dominant water molecules on the spectral line shapes on the rotational line intensity distribution and the ejection pattern of the CN parent molecules at the nucleus surface. Newly derived 13C/12C ratios will be presented and discussed in relation to the likely site of formation of the comets.
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