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 U T January 21.8 and May 1.2, 1997, using high-resolution infrared spectrosco py. This is the first study of the heliocentric dependence of water release d from a comet using direct detection of H2O itself. Production rates and r otational temperatures were measured, and the derived heliocentric dependen ce for the water production rate is Q = (8.35 +/- 0.13) x 10(30) [R-h((-1.8 8+/-0.18))] molecules s(-1). The spatial distribution of H2O molecules in t he coma is consistent with water being released directly from the nucleus w ithin 1.5 AU of the Sun, although release of a small fraction from icy grai ns 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-B opp and, when compared to interstellar and nebular material, helps constrai n the origin of cometary ices and their processing histories. These product ion rates derived from the direct detection of H2O provide a sound basis wi th which water production rates inferred by indirect methods can be compare d. (C) 2000 Academic Press.