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[40.02] Tentative Identification of the Parent of CN radicals in Comets: = C₂N₂

M.C. Festou (SWRI, Boulder, CO), O. Barale (OMP, Toulouse, F), T. Davidge (Dom. Ast. Obs.), S. A. Stern (SWRI, Boulder, CO), G. P. Tozzi (Firenze Obs., It.), M. Womack (St Cloud State Univ., USA), J. M. Zucconi (Besanceon Obs., F)

Although CN is the second species to have been detected in the=20 coma of comets, just after C₂ in 1868, the identification of its=20 precursor has remained since a puzzle. Until now, near-UV photometric=20 profiles and maps of the CN B--X 0--0 band have been interpreted=20 assuming that CN results from the photodestruction of a single=20 (unknown) parent molecule. It has always been found that the=20 putative parent species has a characteristic destruction scale=20 length of order 2\times10⁴ km at 1 A.U. from the Sun. No simple=20 molecule is known to present this characteristic. Observations of comet=20 P/Halley in 1986 showed that coma dust particles contributed =20 to the production of the CN atmosphere, at least in dusty comets,=20 at a not well established level.=20 We have re-examined all the published near-UV observations of the=20 CN radicals and we have complemented our investigation by interpreting=20 new data, namely high dispersion spectra of the CN B--X 0--0 band=20 obtained at various locations inside the coma of comet C/Austin=20 1989c1, a velocity profile of the 2--1 mm-wave lines of CN and maps of=20 the HCN molecule, both obtained in comet C/1995 O1 (Hale-Bopp). A=20 single atmospheric model is used to interpret the entire data set.=20 The data are consistent with one dominant parent species since=20 HCN and CH₃CN are known to contribute at the percent level to=20 the production of CN. The model shows that the=20 scale length found in previous studies is simply a limiting case=20 in which the parent species does not release any energy during their=20 photolysis. Dust particles cannot contribute much either to the=20 formation of the CN coma. Instead, even though no unique solution=20 is found, we can identify a best case for a parent having a=20 lifetime of (3.5 ±0.5) \times 10⁴ s at 1 A.U.=20 and a velocity in the 1--2 km s^-1 range. One molecule=20 presents photolysis characteristics that produce an appropriate=20 CN atmosphere: the chemically stable C₂N₂ molecule.

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The author(s) of this abstract have provided an email address for comments about the abstract: festou@boulder.swri.edu

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