THE SPECTRUM OF COMET HALE-BOPP (C 1995-O1) OBSERVED WITH THE INFRARED SPACE-OBSERVATORY AT 2.9 ASTRONOMICAL UNITS FROM THE SUN/

Comet Hale-Bopp (C/1995 O1) was observed at wavelengths from 2.4 to 19 5 micrometers with the Infrared Space Observatory when the comet was a bout 2.9 astronomical units (AU) from the sun, The main observed volat iles that sublimated from the nucleus ices were water, carbon monoxide , and carbon dioxide in a ratio (by number) of 10:6:2. These species a re also the main observed constituents of ices in dense interstellar m olecular clouds; this observation strengthens the links between cometa ry and interstellar material. Several broad emission features observed in the 7- to 45-micrometer region suggest the presence of silicates, particularly magnesium-rich crystalline olivine. These features are si milar to those observed in the dust envelopes of Vega-type stars.