Tentative Identification of the Parent of CN radicals in Comets: = C_2N_2

Details Tentative Identification of the Parent of CN radicals in Comets: = C_2N_2 Tentative Identification of the Parent of CN radicals in Comets: = C_2N_2

Sep 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998dps....30.4002f&link_type=abstract

American Astronomical Society, DPS meeting #30, #40.02; Bulletin of the American Astronomical Society, Vol. 30, p.1089

Astronomy and Astrophysics

Astronomy

7

Scientific paper

Although CN is the second species to have been detected in the=20 coma of comets, just after C_2 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*E(4) 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 CH_3CN 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) x 10(4) 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 C_2N_2 molecule.

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