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Electron impact excitation of carbon monoxide in comet Hale‐Bopp
Author(s) -
Campbell L.,
Brunger M. J.
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2008gl036641
Subject(s) - comet , carbon monoxide , excitation , physics , coma (optics) , electron , atomic physics , electron ionization , comet tail , astrophysics , abundance (ecology) , chemistry , nuclear physics , solar wind , plasma , quantum mechanics , ion , biochemistry , fishery , biology , ionization , catalysis
The fourth positive emissions of carbon monoxide in the coma of comet Hale‐Bopp have been assumed to be due mainly to fluorescence induced by sunlight. Based on this assumption they were used to deduce the abundance of carbon monoxide in the comet, giving a value higher than in other comets. Emissions produced by electron impact excitation of CO were not considered. Recent measurements and theoretical calculations of integral cross sections for electron impact excitation of CO allow the contribution of electron impact to be calculated, giving about 40% of the total. This implies that the abundance of CO in the outer coma of comet Hale‐Bopp was only 60% of that previously deduced. However, as the high proportion of CO in comet Hale‐Bopp was also seen in some other measurements, alternative explanations are considered. The method of calculation is tested by successfully predicting the O I emission at 1356 Å, supporting the belief that this line is due to electron impact excitation.