THE ACTIVITY AND SIZE OF THE NUCLEUS OF COMET HALE-BOPP (C 1995-01)/

Analysis of Hubble Space Telescope (HST) images of comet Hale-Bopp (C/ 1995 O1) suggests that the effective diameter of the nucleus is betwee n 27 to 42 kilometers, which is at least three times larger than that of comet P/Halley, The International Ultraviolet Explorer and HST spec tra showed emissions from OH (a tracer of H2O) and CS (a tracer of CS2 ) starting in April 1996, and from the CO Cameron system (which primar ily traces CO2) starting in June 1996. The variation of the H2O produc tion rate with heliocentric distance was consistent with sublimation o f an icy body near its subsolar point. The heliocentric variation in t he production rates of CS2 and dust was different from that of H2O, wh ich implies that H2O sublimation did not control the CS2 or dust produ ction during these observations.