ANOMALOUS MOLECULAR ABUNDANCES AND THE DEPLETION OF NH2 IN COMET P/GIACOBINI-ZINNER

Spectrophotometric observations of comet P/Giacobini-Zinner (P/G-Z) were obtained on the nights of 1985 June 17-18, and September 9-13 UT using the Ohio State University Image Dissector Scanner on the Perkins 1.8 m reflector of the Ohio State and Ohio Wesleyan Universities, and the Steward Observatory Pulse Counting Reticon spectrograph on the Steward 2.3 m reflector. We present Haser-model production rates Q for C3, C2, NH2, and CN derived from these data. The ratios Q(C2)/Q(CN) and Q(C3)/Q(CN) were found to be low compared to those in normal comets, indicating that C2 and C3 were underabundant in P/G-Z, in agreement with previous results. More importantly, we also determined Q(NH2)/g(CN) for a sample of five comets to estimate, for the first time, a "normal" value for this ratio. A comparison indicated that Q(NH2)/Q(CN) was low for P/G-Z compared to the ensemble, suggesting that NH2 was underabundant, similar to observed depletions of C2, C3, and NH. We also found that, for our sample of five comets, Q(NH2)/Q(CN) exhibits a strong dependence with heliocentric distance, in contrast to Q(C2)/Q(CN) and Q(C3)/Q(CN). In addition, we present estimates of the dust-to-gas ratio and the quantity Afp from measurements of the reflected solar continuum.