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M. A. DiSanti, D. C. Reuter, M. J. Mumma (NASA-GSFC), N. Dello Russo (Catholic U.@GSFC), K. Magee-Sauer (Rowan U.), E. L. Gibb (NAS-NRC@GSFC), B. P. Bonev (U. Toledo@GSFC), L.-H. Xu (U. New Brunswick)
We have conducted detailed studies of the abundances of parent volatiles in eight Oort cloud comets since 1996, using modern long-slit echelle spectrometers having sensitivity in the 1 -- 5 \mu m region. These instruments (CSHELL at the NASA-IRTF, and NIRSPEC at Keck 2) have sufficiently high spectral resolution ( \nu / \Delta \nu ~ ~~ 2 ~ \times ~ 104 ) to resolve individual cometary emission lines. Their small pixel sizes provide the high angular resolution required for an accurate measure of volatile abundances in the nucleus, as well as for detailed study of the spatial distribution of emissions in the coma.
We routinely characterize the volatile composition of observed comets through measuring the abundances of native ices (H2O, CO, CH3OH, C2H6, CH4, C2H2, and HCN). Here we adapt a fluorescence model for H2CO (Reuter et al. 1989 \it{Ap. J.} \bf{341}, 1045), originally developed for application to low-resolution spectra of 1P/Halley, to our existing sample of cometary spectra. Predicted line g-factors are highly temperature-dependent over the range expected in cometary comae (e.g., ~ 20 -- 150 K). Therefore, we expect application of the model to provide an additional means of measuring rotational temperatures (and hence accurate formaldehyde production rates) in comets. Results for previously observed comets, and detectability limits for future known comets, will be presented.
This work was supported by NASA Planetary Astronomy Program grants NAG5-12208 and RTOP 693-344-32-30-07.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.