The first ISO workshop on analytical spectroscopy with SWS, LWS, PHT-S and CAM-CVF

(Oct 6-8, 1997, Madrid, Spain)

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The Infrared Spectrum of Comet Hale-Bopp

J. Crovisier1 - K. Leech 2 - D. Bockelée-Morvan 1 - T.Y. Brooke 3 -
M.S. Hanner 3 - B. Altieri 2 - H.U. Keller 4 - E. Lellouch 1

1 Observatoire de Paris-Meudon, F-92195 Meudon, France
2 ISO Science Operations Centre, Astrophysics Division of ESA, Villafranca, Spain
3 Jet Propulsion Laboratory, Pasadena, USA
4 MPI für Aeronomie, Katlenburg-Lindau, Germany

Spectra of comet C/1995 O1 (Hale-Bopp) were observed at medium resolution with PHT-S and at high resolution with the long- and short-wavelength spectrometers of the Infrared Space Observatory on September-October 1996, when the comet was at about 3 AU from the Sun. For the first time, a high-resolution spectrum of a comet covering the entire 2.4 to 200 tex2html_wrap_inline26m spectral range was obtained.

The vibrational bands of water, carbon dioxide and carbon monoxide are detected in emission with PHT-S, as expected from molecular fluorescence models. Relative production rates of 100:22:70 are derived for Htex2html_wrap_inline28O:COtex2html_wrap_inline28:CO. Htex2html_wrap_inline28O is observed at high spectral resolution in the tex2html_wrap_inline34 group of bands around 2.7 tex2html_wrap_inline26m and the tex2html_wrap_inline38 group around 6 tex2html_wrap_inline26m with SWS, and in a couple of rotational lines near 180 tex2html_wrap_inline26m with LWS. The rovibrational lines of the tex2html_wrap_inline34 band are observed with a high signal-to-noise ratio. This allows accurate determinations of the water rotational temperature and of its ortho-to-para ratio.

Longward of 6 tex2html_wrap_inline26m, the spectrum is dominated by dust thermal continuum emission, upon which broad emission features are superimposed. The wavelengths of the emission peaks correspond to those of Mg-rich crystalline olivine (forsterite).

Highlights of these results were briefly reported in Crovisier et al. (1997). We will present the latest developments of their analysis.

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