2D photochemical model for forbidden oxygen line emission for comet 1P/Halley

We present here a 2D model of photochemistry for computing the production and loss mechanisms of the O(S-1) and O(D-1) states, which are responsible for the emission lines at 577.7, 630, and 636.4 nm, in case of the comet 1P/Halley. The presence of O-2 within cometary atmospheres, measured by the in situ Rosetta and Giotto missions, necessitates a revision of the usual photochemical models. Indeed, the photodissociation of molecular oxygen also leads to a significant production of oxygen in excited electronic states. In order to correctly model the solar ultraviolet (UV) flux absorption, we consider here a 2D configuration. While the green to red-doublet ratio is not affected by the solar UV flux absorption, estimates of the red-doublet and green lines emissions are, however, overestimated by a factor of 2 in the 1D model compared to the 2D model. Considering a spherical symmetry, emission maps can be deduced from the 2D model in order to be directly compared to ground and/or in situ observations.