FLUORESCENCE EXCITATION MODELS OF AMMONIA AND AMIDOGEN RADICAL (NH{sub 2}) IN COMETS: APPLICATION TO COMET C/2004 Q2 (MACHHOLZ)

Journal Article · Tue Feb 01 04:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/727/2/91· OSTI ID:21567545

Kawakita, Hideyo ^[1]

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1. Department of Physics, Faculty of Science, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555 (Japan)

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 {mu}m wavelength region), but moderate relative velocity shifts are required to separate emission lines of cometary ammonia from telluric absorption lines in the 3 {mu}m wavelength region. On the other hand, the amidogen radical (NH{sub 2}-a photodissociation product of ammonia in the coma) also shows rovibrational emission lines in the 3 {mu}m 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{sub 3} lines, the mixing ratio of NH{sub 3}/H{sub 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{sub 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{sub 3} could be the sole parent of NH{sub 2} in this comet.

• OSTI ID: 21567545
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 727; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
AMMONIA
COMETS
DETECTION
DIMENSIONLESS NUMBERS
DISSOCIATION
ELECTROMAGNETIC RADIATION
EMISSION
ENERGY-LEVEL TRANSITIONS
EXCITATION
FLUORESCENCE
HYDRIDES
HYDROGEN COMPOUNDS
INFRARED RADIATION
LUMINESCENCE
MIXING RATIO
NEAR INFRARED RADIATION
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
PHOTON EMISSION
RADIATIONS
RADICALS