Co-adding of the brightest (3,0) and (2,0) emission lines of ¹³CO⁺ (left) and ¹²CO⁺ (right) with the corresponding modeling (see Table 4 for the detailed list of co-added lines). Both figures display the co-added CO⁺ lines with their surroundings at a high signal-to-noise ratio. The features seen – especially for ¹³CO⁺, which has a lower intensity scale – are then most probably real features above the one-sigma noise level appearing on the left part of this plot.