Astronomy and Astrophysics – Astronomy
Scientific paper
May 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003dps....35.3808d&link_type=abstract
American Astronomical Society, DPS meeting #35, #38.08; Bulletin of the American Astronomical Society, Vol. 35, p.985
Astronomy and Astrophysics
Astronomy
Scientific paper
Water is the dominant ice in comets, and its sublimation controls the release of other volatiles within 3-4 AU of the sun. Accurate measurements of H2O abundances are important for determining the relative volatile fractions in comets since the volatile activity of a comet and the abundances of minor species are often expressed relative to H2O production. Targeting water lines from the ground at infrared wavelengths is a proven method for obtaining accurate H2O production rates since in general multiple lines can be observed simultaneously. In addition, observations from the ground allow coverage over a range of heliocentric distances. To avoid the atmospheric extinction that prevents the detection of strong H2O lines from fundamental bands, we target (weaker) lines seen in non-resonance fluorescence. The detection of these lines requires no specific geocentric Doppler-shift for the comet. This approach has been successfully used to detect water lines from the ground in comets since the early 1990s. The 2.9-micron spectral region is particularly diagnostic since a dense grouping of strong lines can be detected from several different hot-bands.
We have developed line-by-line temperature-dependent fluorescence models for seven hot-bands near 2.9-microns. Here we compare our models to high-resolution comet data obtained with the Near Infrared Spectrometer (NIRSPEC) at Keck 2 and the Cryogenic Echelle Spectrometer (CSHELL) at the NASA IRTF (R ˜ 20,000 for both instruments). We discuss H2O production rates, rotational temperatures, and ortho-to-para ratios for several comets within our current database (e.g. C/1999 H1 (Lee), C/1999 S4 (LINEAR), C/2001 A2 (LINEAR), and C/2002 C1 (Ikeya-Zhang)), and we predict line intensities and detectability limits for H2O in comet 2P/Encke in November 2003.
This work was supported by the NASA Planetary Atmospheres Program (NAG5-10795), and the NASA Planetary Astronomy Program (RTOP 693-344-32-30-07).
Barber Robert J.
Bonev Boncho P. .
Dello Russo Neil
DiSanti Michael A.
Gibb Erika Lynne
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