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Title: MONTE CARLO SIMULATION OF METASTABLE OXYGEN PHOTOCHEMISTRY IN COMETARY ATMOSPHERES

Cometary atmospheres are produced by the outgassing of material, mainly H{sub 2}O, CO, and CO{sub 2} from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical processes lead to the production of other species generally absent from the nucleus, such as OH. Although all comets are different, they all have a highly rarefied atmosphere, which is an ideal environment for nonthermal photochemical processes to take place and influence the detailed state of the atmosphere. We develop a Monte Carlo model of the coma photochemistry. We compute the energy distribution functions (EDF) of the metastable O({sup 1}D) and O({sup 1}S) species and obtain the red (630 nm) and green (557.7 nm) spectral line shapes of the full coma, consistent with the computed EDFs and the expansion velocity. We show that both species have a severely non-Maxwellian EDF, that results in broad spectral lines and the suprathermal broadening dominates due to the expansion motion. We apply our model to the atmosphere of comet C/1996 B2 (Hyakutake) and 103P/Hartley 2. The computed width of the green line, expressed in terms of speed, is lower than that of the red line. This result is comparable to previous theoretical analyses, but inmore » disagreement with observations. We explain that the spectral line shape does not only depend on the exothermicity of the photochemical production mechanisms, but also on thermalization, due to elastic collisions, reducing the width of the emission line coming from the O({sup 1}D) level, which has a longer lifetime.« less
Authors:
;  [1] ; ;  [2] ; ;  [3] ;  [4] ;  [5]
  1. Institute of Astronomy of the Russian Academy of Sciences, Moscow (Russian Federation)
  2. Laboratory for Planetary and Atmospheric Physics (LPAP), University of Liège, Liège (Belgium)
  3. Origines Cosmologiques et Astrophysiques (ORCA), University of Liège (Belgium)
  4. Extragalactic Astrophysics and Space Observations (EASO), University of Liège (Belgium)
  5. High Energy Astrophysics Group (GAPHE), University of Liège (Belgium)
Publication Date:
OSTI Identifier:
22364760
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 798; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON DIOXIDE; CARBON MONOXIDE; COMETS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; ENERGY SPECTRA; LIFETIME; MONTE CARLO METHOD; OXYGEN; PHOTOCHEMISTRY; SATELLITE ATMOSPHERES; SUN; THERMALIZATION