EVOLUTION OF THE OUTGASSING OF COMET HALE-BOPP (C 1995-O1) FROM RADIOOBSERVATIONS/

Spectra obtained from ground-based radio telescopes show the progressi ve release of CO, CH3OH, HCN, H2O (from OH), H2S, CS, H2CO, CH3CN, and HNC as comet Hale-Bopp (C/1995 O1) approached the sun from 6.9 to 1.4 astronomical units (AU). The more volatile species were relatively mo re abundant in the coma far from the sun, but there was no direct corr elation between overabundance and volatility. Evidence for H2O sublima tion from icy grains was seen beyond 3.5 AU from the sun. The change f rom a GO-driven coma to an H2O-driven coma occurred at about 3 AU. The gas outflow velocity and temperature increased as Hale-Bopp approache d the sun.