The HNC/HCN Ratio in Comets |
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Authors: | Irvine W M Dickens J E Lovell A J Schloerb F P Senay M Bergin E A Jewitt D Matthews H E |
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Institution: | (1) Five College Radio Astronomy Observatory, University of Massachusetts, Amherst, MA 01003, USA;(2) Smithsonian Astrophysical Observatory, 60 Garden St., Cambridge, MA 02138-1596, USA;(3) Institute for Astronomy, Univ. of Hawaii, Honolulu, HI 96822, USA;(4) Joint Astronomy Centre, Hilo, HI 96720, USA |
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Abstract: | The abundance ratio of the isomers HCN and HNC has been investigated in comet Hale-Bopp (C/1995 O1) through observations of
the J = 4−3 rotational transitions of both species for heliocentric distances 0.93 < r < 3 AU, both pre- and post-perihelion.
After correcting for the optical depth of the stronger HCN line, we find that the column density ratio of HNC/HCN in our telescope
beam increases significantly as the comet approaches the Sun. We compare this behavior to that predicted from an ion-molecule
chemical model and conclude that the HNC is produced insignificant measure by chemical processes in the coma; i.e., for comet
Hale-Bopp, HNC is not a parent molecule sublimating from the nucleus.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | Comets interstellar molecules |
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