The Spectrum of Comet Hale-Bopp as seen by ISO

Details The Spectrum of Comet Hale-Bopp as seen by ISO The Spectrum of Comet Hale-Bopp as seen by ISO

Mar 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999esasp.427..137c&link_type=abstract

The Universe as Seen by ISO. Eds. P. Cox & M. F. Kessler. ESA-SP 427., p. 137

Physics

19

Comets, C/1995 O1 (Hale-Bopp), Dust, Molecules, Spectroscopy

Scientific paper

Comet C/1995 O1 (Hale-Bopp) was observed with the Infrared Space Observatory within the target-of-opportunity comet programme. Spectra were obtained pre-perihelion on April 1996 and September-October 1996, and post-perihelion on December 1997 and April 1998, spanning heliocentric distances (r) between 2.8 and 4.9 AU. At the largest r's, only PHT-S spectra were obtained. At the smallest r's, a high-resolution spectrum covering the full 2.4 to 195 μm spectral range was obtained for the first time in a comet, using SWS and LWS. Spectra of dedicated regions (H2O, CO and CO2 bands) were also observed with SWS. The vibrational bands of water, carbon dioxide and carbon monoxide are detected in emission, as expected from molecular fluorescence models. Relative production rates for H2O:CO2:CO vary, as a function of r, as could be expected from the different volatilities of these species. H2O was observed at high spectral resolution in the ν3 group of bands around 2.7 μm, the ν2 group around 6 μm with SWS, and in several rotational lines with LWS. The ro-vibrational lines of the ν3 band were observed with a high S/N in September-October 1996. This allows an accurate determination of the water rotational temperature (28 K) and of its ortho-to-para ratio (2.45 +/- 0.10), which significantly differs from the high temperature limit and corresponds to a spin temperature of 25 K). Longward of 6 μm, the spectrum is dominated by dust thermal continuum emission, upon which broad emission features are superimposed whose peak wavelengths correspond to those of Mg-rich crystalline olivine (forsterite). In the September-October spectra, emission features at 44 and 65 μm and possible absorption at 2.9-3.2 μm suggest that grains of water ice were present at 2.9 AU from the Sun.

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