A taxonomic survey of comet composition 1985-2004 using CCD spectroscopy

A summary is presented of our spectroscopic survey of comets extending for roughly 19 years from 1985 to 2004 comprising data for 92 comets of which 50 showed good emissions. All data were re-analyzed rising consistent reduction techniques. Our observations of cornets over several apparitions and comets observed over all extended period indicate no major changes in compositional classification. To our regret, no major unidentified cometary features were found in our surveyed spectral region of 5200-10400 A. Absolute production rates for the dominant patent molecule H2O and the daughter Species C-2, NH2 and CN are determined within the limits of the Haser model as are values for the dust continuum, Af rho. From these data, production rate ratios are calculated for C-2/H2O, NH2/H2O, CN/H2O and Af rho/H2O. Excluding the odd Comets Yanaka (1988r), 43P/Wolf-Harrington and 19P/Borrelly, with unusual spectra, out set of comets exhibited relatively uniform composition. Detailed analyses of our data resulted in four taxonomic classes: - Connets of typical composition (similar to 70%): exhibiting typical ratios with respect to water of C-2, NH2 , and CN. - Tempel 1 type (similar to 22%); having a deficiency in C-2 but normal NH2 abundance. - G-Z type (similar to 6%): having both low C-2 and NH2 ratios. - The unusual object Yanaka (1988r) (similar to 2%?): no detectable C-2 or CN emission but normal NH2. It is uncertain whether there is a clear separation between the comets of typical composition and those with C-2 depletion, or whether the latter consists of a group showing a continuum of decreasing C-2/CN ratios. Our spectroscopic investigations result in a Visual record of the various compositional classes, which are illustrated in a number of figures. Production rate comparisons with the comet photometry program of Schleicher and A'Hearn [A'Hearn, M.F., and 4 colleagues, 1995. Icarus 118, 223-270] for 13 comets in common yielded good agreement once the different scale lengths are taken into account. All investigation into the possible origin of our compositional groups with respect to dynamical families of comets shows that the Halley family exhibits essentially 110 C2 depletion, These objects were presumably formed in the region of Saturn and Uranus and scattered into the Oort cloud. Comets formed in the space near Neptune, responsible for the scattered Kuiper Belt show a mixture of typical and C, depleted objects, while we associate cornets formed in-situ in the classical Kuiper belt with our C-2 depleted group. (c) 2009 Elsevier Inc. All rights reserved,