A Spitzer IRS Study of Comets 71P/Clark and C/2004 B1 (LINEAR): Water, Carbonates, PAHs

Details A Spitzer IRS Study of Comets 71P/Clark and C/2004 B1 (LINEAR): Water, Carbonates, PAHs A Spitzer IRS Study of Comets 71P/Clark and C/2004 B1 (LINEAR): Water, Carbonates, PAHs

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21340104w&link_type=abstract

American Astronomical Society, AAS Meeting #213, #401.04; Bulletin of the American Astronomical Society, Vol. 41, p.189

Astronomy and Astrophysics

Astronomy

Scientific paper

Production rates of volatiles are used to quantify cometary activity and to measure volatile abundances. Water is the dominant ice in cometary nuclei and its sublimation governs the activity of comets at heliocentric distances, < 3 AU from the Sun. Here we discuss Spitzer Space Telescope IRS 5.5 to 7.6 micron spectra of comets 71P/Clark obtained on 2006 May 27.56 UT, at a pre-perihelion distance of 1.57 AU and C/2004 B1 (LINEAR) obtained at two different epochs: 2005 October 15.22 UT, pre-perihelion at a heliocentric distance of 2.21 AU, and post-perihelion at 2.06 AU on 2006 May 16.22 UT. The nu2 vibrational band of water is detected with a signal-to-noise ratio of 11 to 40. Fitting the spectra using a fluorescence model of water emission yields a water rotational temperature of < 18 K for 71P/Clark and 14 ± 2 K (pre-perihelion) and 23 ± 4 K (post-perihelion) for C/2004 B1 (LINEAR). Water production rates and water ortho-to-para ratios (OPR) are derived. The agreement between the water model and the measurements is good, as previously found for Spitzer spectra of C/2003 K4 (LINEAR) (e.g., Woodward et al. 2007, ApJ, 671, 1065). The Spitzer spectra of these three comets do not show any evidence for emission from PAHs and carbonate minerals, in contrast to results reported (e.g., Lisse et al. 2007, Icarus 187, 69 as reviewed by Crovisier and Bockelee-Morvan 2008, Icarus 195, 938) for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp).
Support for this work provided in part by NASA through contracts 1263741, 1256406, and 1215746 issued by JPL/Caltech to the University of Minnesota, and the National Science Foundation grant AST-0706980.

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