A SURVEY OF 39 COMETS USING CCD SPECTROSCOPY

摘要

An analysis of our spectra of 39 comets from 0.55 to 1.0 μm collected over the last decade is presented. All spectra were obtained with the 154 cm Mount Bigelow telescope of the University of Arizona Observatories, using our fast f/1.2 spectrograph and an 800 x 800 TI CCD detector. Roughly 21 of the objects observed displayed emissions while the other 18 simply yielded a continuum, although three of these gave a suggestion of possible CN emission. Emission fluxes were measured for the Δv = — 1 C_2 Swan band, the 0,10,0 and 0,8,0 NH_2 bands, the O I ~1D line at 6300 A and the red CN system 2-0 and 1-0 bands. From these fluxes, production rates for the parents of C_2, NH_2, O I, and CN were deter-mined and mixing ratios of the parents of C_2, NH_2, and CN with respect to H_2O were calculated. We estimate our standard deviation error in these numbers to be about 10%. We find that about 10% of the comets have deviant composition with the most common being the P/Giacobini-Zinner class and the most unusual represented by Yanaka (1988r). The other 90% of our comet sample shows reasonably uniform mixing ratios with maximum comet-to-comet variations of a factor of 2-3 and a standard deviation of ～30%. No distinct compositional classes could be discerned within that group. We interpret the observed spread in production rate ratios as chemical composition variations between individual comets and a measure of the nonuniformity of the solar nebula during the time of the solar system formation.