Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.5603w&link_type=abstract
American Astronomical Society, AAS Meeting #211, #56.03; Bulletin of the American Astronomical Society, Vol. 39, p.828
Physics
Scientific paper
Water is the dominate ice in comet nuclei. Probed through spectroscopic observations of coma species, the water production rate, coma temperature, and the nuclear spin temperatures derived from ortho-to-para ratios (OPR) are of particular interest in the study of cometary atmospheres and cometary physics. These physical characteristics, complemented by knowledge of the nucleus refractory and ice composition, provide constraints on solar nebula models and restrict the formation zones within the protoplanetary disk where cometary nuclei could conglomerate. We discuss sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR) obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The nu2 vibrational band of water is detected with a high signal-to-noise ratio (>50). Model fitting to the best spectrum yields a water OPR of 2.47 ± 0.27, which corresponds to a spin temperature of 28.5 (+6.5/-3.5) K. Spectra acquired at different offset positions show that the rotational temperature decreases with increasing distance from the nucleus, which is consistent with evolution from thermal to fluorescence equilibrium. The inferred water production rate is (2.43 ± 0.25) e+29 molec. s-1. In addition, our models of the nu2 band H20 fluorescence emission shows that water wholly accounts for any emission in-excess of the continuum at wavelengths where organic (PAHs, 6.2 micron) or carbonate species (7 micron) would emit, in contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp).
Support for this work provided by NASA through contracts 1263741, 1256406, and 1215746 issued by JPL/Caltech to the University of Minnesota, and the NSF through grant AST-037446.
Bockelée-Morvan Dominique
Kelley Michael
Woodward Charles E.
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