Thursday 17 September at 11am

Nicolas Biver - JCMT Fellow - Institute for Astronomy

"Comets Hyakutake and Hale-Bopp long term monitorings at radio wavelengths"

ABSTRACT:"Comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp) have offered exceptional opportunities to follow the evolution of the gaseous activity of a comet on a wide range of heliocentric distances (0.25 to 1.8 AU and 0.9 to 7 AU respectively). They have been monitored at mm to sub-mm wavelengths using JCMT, IRAM, CSO and SEST radiotelescopes. I will put emphasize on the main results as regards the evolution of key parameters such as the temperature of the coma and its expansion velocity, and molecular abundances versus heliocentric distance. The most important result concerns the evolution of the relative abundances of the species as a function of heliocentric distance. Observations of comets Hyakutake and Hale-Bopp have provided complementary results, namely as regards the CS/HCN, H2CO/HCN and HNC/HCN ratios. In addition, the study of comet Hale-Bopp beyond 3 AU has shown that the sublimation of CO is the major driver of the comet activity, and that other minor species such as HCN and CH3OH have a much more volatile behaviour than H2O, the main component of cometary ices."