Water Production and Release in Comet C/1995 O1 Hale-Bopp

Water (H₂O) was detected in Comet C/1995 O1 Hale-Bopp on 10 dates between UT January 21.8 and May 1.2, 1997, using high-resolution infrared spectroscopy. This is the first study of the heliocentric dependence of water released from a comet using direct detection of H₂O itself. Production rates and rotational temperatures were measured, and the derived heliocentric dependence for the water production rate is Q=(8.35±0.13)×10³⁰ [R_h^{(-1.88±0.18)}] molecules s^-1. The spatial distribution of H₂O molecules in the coma is consistent with water being released directly from the nucleus within 1.5 AU of the Sun, although release of a small fraction from icy grains cannot be excluded. When our derived water production rates are compared to the production of native carbon monoxide and dust, we obtain a dust to ice mass ratio of 5.1±1.2 within a heliocentric distance of 1.5 AU. The abundance of H₂O provides a benchmark for the volatile inventory in Hale-Bopp and, when compared to interstellar and nebular material, helps constrain the origin of cometary ices and their processing histories. These production rates derived from the direct detection of H₂O provide a sound basis with which water production rates inferred by indirect methods can be compared.