N+2 and CO+ in Comets 122P/1995 S1 (deVico) and C/1995 O1 (Hale–Bopp)

McDonald Observatory, University of Texas at Austin, Austin, Texas, 78712, .utexas.eduf1
Icarus (Impact Factor: 3.04). 03/2000; 146(2):583-593. DOI: 10.1006/icar.2000.6413
Source: arXiv


We observed Comets 122P/1995 S1 (deVico) and C/1995 O1 (Hale–Bopp) with high spectral resolving power in order to determine the ratio of N+2/CO+ in their comae. While we clearly detected the CO+ in both of these comets, no N+2 was detected in either comet. From these spectra, we derive sensitive upper limits for N+2/CO+. These upper limits are substantially below other reported detections of N+2/CO+ in other comets. We discuss the prior N+2 detections and compare them with our observations. The abundance of N2 in comets is important to our understanding of the condensation of ices in the solar nebula. In addition, N2 is a tracer of Ar so the study of N2 allows an understanding of the role of comets for delivering volatiles to the terrestrial planets. It appears that many, if not most, comets are depleted in N2 and it will be necessary to search for a mechanism for depleting this molecule in order to be consistent with current models of the solar nebula.

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    ABSTRACT: The composition of cometary ices provides key information on the chemical and physical proper- ties of the outer solar nebula where comets formed, 4.6 Gyr ago. This chapter summarizes our current knowledge of the volatile composition of cometary nuclei, based on spectroscopic observations and in situ measurements of parent molecules and noble gases in cometary comae. The processes that govern the excitation and emission of parent molecules in the radio, infrared (IR), and ultraviolet (UV) wavelength regions are reviewed. The techniques used to convert line or band fluxes into molecular production rates are described. More than two dozen parent molecules have been identified, and we describe how each is investigated. The spatial distribution of some of these molecules has been studied by in situ measure- ments, long-slit IR and UV spectroscopy, and millimeter wave mapping, including interferometry. The spatial distributions of CO, H CO, and OCS differ from that expected during direct sublimation from the nucleus, which suggests that these species are produced, at least partly, from extended sources in the coma. Abundance determinations for parent molecules are reviewed, and the evidence for chemical diversity among comets is discussed.
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    ABSTRACT: Many new cometary molecules — both parents and daughters — were detected in the exceptionally productive comet C/1995 O1 (Hale-Bopp).The space distribution of several of these species could be investigated from radio interferometry or from long-slit spectroscopy in the infrared. The distinction between parent species — directly sublimated from nucleus ices — and secondary species — resulting from chemical processing in the coma or produced by a secondary source — is not always clear. It is important to assess whether or not observed minor species (HCOOCH3, HCOOH...) could be synthesized by chemical reactions favoured by the high density of the coma of comet Hale-Bopp. Chemical modelling by Rodgers and Charnley suggests that this is notthe case. CO and H2CO are abundant cometary species which partly come from distributed sources. The nature of these sources is still a mystery. A special case, now well documented, is that of HNC, for which the abundance evolution with heliocentric distance could be observed in comet Hale-Bopp and which was observed in several much less productive comets.
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