The Activity and Size of the Nucleus of Comet Hale-Bopp (C/1995 O1)

Abstract
Analysis of Hubble Space Telescope (HST) images of comet Hale-Bopp (C/1995 O1) suggests that the effective diameter of the nucleus is between 27 to 42 kilometers, which is at least three times larger than that of comet P/Halley. The International Ultraviolet Explorer and HST spectra showed emissions from OH (a tracer of H 2 O) and CS (a tracer of CS 2 ) starting in April 1996, and from the CO Cameron system (which primarily traces CO 2 ) starting in June 1996. The variation of the H 2 O production rate with heliocentric distance was consistent with sublimation of an icy body near its subsolar point. The heliocentric variation in the production rates of CS 2 and dust was different from that of H 2 O, which implies that H 2 O sublimation did not control the CS 2 or dust production during these observations.