FLUORESCENCE EXCITATION MODELS OF AMMONIA AND AMIDOGEN RADICAL (NH{sub 2}) IN COMETS: APPLICATION TO COMET C/2004 Q2 (MACHHOLZ)
- 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, Vol. 727, Issue 2; Other Information: DOI: 10.1088/0004-637X/727/2/91; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AMMONIA
COMETS
DETECTION
DISSOCIATION
EXCITATION
FLUORESCENCE
MIXING RATIO
NEAR INFRARED RADIATION
RADICALS
DIMENSIONLESS NUMBERS
ELECTROMAGNETIC RADIATION
EMISSION
ENERGY-LEVEL TRANSITIONS
HYDRIDES
HYDROGEN COMPOUNDS
INFRARED RADIATION
LUMINESCENCE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
PHOTON EMISSION
RADIATIONS