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| Titel |
Molecular emission spectral line shape analysis in cometary coma using Direct Simulation Monte Carlo (DSMC) methods: What can be learned from observations of the line shapes? |
| VerfasserIn |
Paul von Allmen, Seungwon Lee, Samuel Gulkis, Mark Hofstadter, Mathieu Choukroun, Stephen Keihm, Michael Janssen, Pierre Encrenaz |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099440
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| Publikation (Nr.) |
 EGU/EGU2014-15220.pdf |
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| Zusammenfassung |
| The line shape of molecular emission in a cometary coma is determined in part by the distribution of the molecular velocity and rotational level population. It is commonly believed that close to the cometary nucleus, there is a transition region in the coma, called the Knudsen layer, in which the velocity distribution of the gas is non-Maxwellian (W. Huebner and W. Markiewicz, 2000, Icarus, 148, 594-596). Similarly, in regions where molecular collisions are rare the rotational level distribution differs from the Boltzmann distribution and non-local thermal equilibrium effects determine the molecular emission line shape. We have used the Direct Simulation Monte Carlo method to determine the velocity and rotational level distributions for low-lying ground state transitions throughout the coma, and computed the resulting emission line shape for the isotopologues of H2O with observational parameters close to those for the MIRO instrument on the Rosetta spacecraft en route to 67P/Churyumov-Gerasimenko. We will discuss the effects of heliocentric distance, diurnal and seasonal variations, and how observations of non-Maxwellian spectral line shapes in the Knudsen region and elsewhere, can be used to infer physical properties of the nucleus and coma. |
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