Near-infrared Emission Lines Of NH2 In Comets: Comparison Of Production Rates Of Ammonia And NH2 In Comet C/2004 Q2 (Machholz) And Implications For A General Application.

Details Near-infrared Emission Lines Of NH2 In Comets: Comparison Of Production Rates Of Ammonia And NH2 In Comet C/2004 Q2 (Machholz) And Implications For A General Application. Near-infrared Emission Lines Of NH2 In Comets: Comparison Of Production Rates Of Ammonia And NH2 In Comet C/2004 Q2 (Machholz) And Implications For A General Application.

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.1504k&link_type=abstract

American Astronomical Society, DPS meeting #41, #15.04

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Scientific paper

Ammonia is a major reservoir of nitrogen atoms in cometary materials. However, observations of ammonia are hampered by poor telluric transmittance in the infrared or by lack of spatial resolution (dilution effect) in the radio domain. Although high-dispersion spectroscopic observations in the near-infrared can provide access to ammonia emission lines associated with its ro-vibrational transitions (ν1 band), usually only a small number of lines can be sampled because of poor atmospheric transmittance.
The photo-dissociation process of ammonia by solar UV radiation in the coma would produce NH2 efficiently, but other parents of NH2 might also exist in comets. Fortunately, NH2 emission lines can be sampled directly in its near-infrared vibrational bands (ν1 and ν3). The presence of a second source of NH2 can be tested by comparing the NH2 production rate inferred from its own emission lines with the production rate predicted from NH3 (measured separately). In the absence of an NH3 measurement, NH2 can provide an important marker for estimating the maximum ammonia abundance in a comet. However, until now there has been no excitation model for the near-infrared emission lines of NH2 in comets.
We formulated quantitative g-factors (fluorescence efficiencies) for the near-infrared emission lines of NH2 (ν1 and ν3), taking into account the ro-vibronic transitions of NH2 caused by Fermi-type resonance. We applied these g-factors to lines of NH2 in comet C/2004 Q2 (Machholz). The quantitative production rate obtained from NH2 agrees with that obtained from a fluorescence analysis of NH3 emission lines (with dissociative yield of NH2) in Q2, supporting the view that NH3 is the sole parent of NH2 in this comet. The new approach permits a general test of NH2 production in comets from parent volatiles other than NH3, and thus a test of possible additional reservoirs for atomic nitrogen in the cometary nucleus.

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