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[38.12] Chemistry of NS and CS in Cometary Comae

M. V. Canaves, A. A. de Almeida (IAG/USP), D. C. Boice (SwRI), G. C. Sanzovo (UEL)

The most fundamental scientific reason for studying comets is to retrieve information on their origin, which gives clues of their relationship to interstellar and interplanetary material and implications for the formation of the Solar System. The determination of the basic parameters of the nucleus, its activity and composition is necessary to establish a unique description of the physical-chemical nature of the nucleus. The chemistry of both nitrogen and sulfur presents interesting problems in comets. In this work, we use a model of cometary coma with gas-phase chemical kinetics and gas dynamics in the inner coma region for two of the brightest comets in the past 20 years, C/Hyakutake (1996 B2) and C/Hale-Bopp (1995 O1), with the purpose to predict the abundances of nitrogen sulfide (NS) and carbon monosulfide (CS).

The determination of the abundance of each such species helps to constrain the sulfur chemistry and physical processes and hence their place and mode of origin of the nucleus. The model is applied at a heliocentric distance of 1 AU using a detailed photo and chemical reaction network including more than 100 species and over 1000 reactions. The collisional reactions have up-to-date rate coefficients from Le Teuff, Millar & Markwick (A&A 146, 157-168, 2000), while the photolytic rate coefficients were taken for minimum and maximum solar fluxes in order to estimate a lower and an upper limit for the abundances of NS and CS. The comparision of results for the NS molecule, recently found in comet C/Hale-Bopp (1995 O1) is in very good agreement with Irvine et al. (Icarus 143, 412-414, 2000), while for CS species we show that the abundances do not seem to vary much with the cometocentric distance.

This work was supported by grants from FAPESP (Brazil) 99/07372-1 and NSF 9973186.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.