2D-photochemical model for forbidden oxygen line emission for comets

Emissions at 577.7 nm (green line), 630 nm, and 636.4 nm (red-doublet) come from the deactivation of the O(1S) and O(1D) oxygen states. The photodissociation of H2O, CO and CO2 in the inner coma are responsible for the production of those oxygen states. This list of species had to be extended to include molecular oxygen since its in-situ detection by the Rosetta and Giotto missions. This contribution will present a 2D-photochemical model that calculates the number densities of the O(1S) and O(1D) oxygen states in the comae of various comets, taking the production, the loss and the transport mechanisms into account. For very active comets, e.g. 1P/Halley, a 1D model does not suffice since the solar UV flux is strongly absorbed resulting in an overestimation of the red-doublet and green lines emissions by a factor of 2. Even when assuming spherical symmetry of the neutral gas coma, the phase angle of the observation introduces asymmetries in the measured emission line ratios. Emission maps are deduced from our 2D-model, which can directly be compared to ground and/or in-situ observations.