Publication


H. Kawakita, et al.
Fluorescence Excitation Models of Ammonia and Amidogen Radical (NH2) in Comets: Application to Comet C/2004 Q2 (Machholz)
The Astrophysical Journal, 727(2), 91-102, 2011
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Abstract


Ammonia is a major reservoir of nitrogen atoms in cometary materials. However, detections of ammonia in comets are rare, with several achieved at radio wavelengths. A few more detections were obtained through near-infrared observations (around the 3 μm wavelength region), but moderate relative velocity shifts are required to separate emission lines of cometary ammonia from telluric absorption lines in the 3 μm wavelength region. On the other hand, the amidogen radical (NH 2 —a photodissociation product of ammonia in the coma) also shows rovibrational emission lines in the 3 μm wavelength region. Thus, gas production rates for ammonia can be determined from the rovibrational emission lines of ammonia (directly) and amidogen radical (indirectly) simultaneously in the near-infrared. In this article, we present new fluorescence excitation models for cometary ammonia and amidogen radical in the near-infrared, and we apply these models to the near-infrared high-dispersion spectra of comet C/2004 Q2 (Machholz) to determine the mixing ratio of ammonia to water in the comet. Based on direct detection of NH 3 lines, the mixing ratio of NH 3 /H 2 O is 0.46% ± 0.03% in C/2004 Q2 (Machholz), in agreement with other results. The mixing ratio of ammonia determined from the NH 2 observations (0.31%-0.79%) is consistent but has relatively larger error, owing to uncertainty in the photodissociation rates of ammonia. At the present level of accuracy, we confirm that NH 3 could be the sole parent of NH 2 in this comet.

Reference


@article{0004-637X-727-2-91,
  author = "H. Kawakita and M. J. Mumma",
  title = "Fluorescence Excitation Models of Ammonia and Amidogen Radical (NH2) in Comets: Application to Comet C/2004 Q2 (Machholz)",
  year = 2011,
  journal = "The Astrophysical Journal",
  volume = 727,
  number = 2,
  pages = "91-102",
  month = "Jan",
  url = "http://stacks.iop.org/0004-637X/727/i=2/a=91"
}
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