THE CO2 CO ABUNDANCE RATIO IN 1P/HALLEY AND SEVERAL OTHER COMETS OBSERVED BY IUE AND HST/

We report the detection of CO Cameron band emission in the ultraviolet spectra of four moderately active comets (including 1P/Halley) obtain ed by the International Ultraviolet Explorer (IUE) satellite. The moti vation was the observation of Cameron band emission, a tracer of the C O, production rate, in the spectra of two comets observed by the Hubbl e Space Telescope (HST). We examined IUE spectra of those comets for w hich CO Fourth Positive emission was detected so that the CO productio n rate could be derived simultaneously Also, we used the (1, 0) band a t 1993 Angstrom, at the extreme end of the spectral range of the short -wavelength prime (SWP) spectrograph rather than the (0, 0) or (0, 1) bands at 2063 and 2155 Angstrom, respectively, which fall at the low-s ensitivity end of the long-wavelength camera. For 1P/ Halley, the CO2 production rate that we derive, based on a (1, 0) Cameron band emissio n observation made by IUE at the time of the Giotto encounter, is in g ood agreement with the in situ result. With the exception of comet Lev y, the production rate of CO, relative to water in all of these comets is found to have a value close to that found for 1P/Halley. However, the two comets observed by HST appear to be deficient in CO (but not i n CO2) relative to those observed by IUE. Since these two comets had l ower water production rates than any of those observed by IUE, this su ggests, albeit from a very small sample, that the overall level of act ivity of a comet may be related to its relative CO abundance.