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Fig. 7

image

Column density ratio of CH+ to OH+ vs. gas temperature for several chemical toy models (densities given above the figures) for FUV irradiation without X-rays (top) and X-ray irradiation without FUV (bottom). The radiation levels are color coded. The range of observed values for absorption lines is shaded. The excitation temperature for CH+ from 1D slab model fitting of emission lines (Table B.1) is indicated with a blue dot.

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