Left: colour scale map of the C¹⁸O opacity calculated from the ratio of ¹³CO to C¹⁸O emission. The C¹⁸O optical depth is less than 0.5 in most of the cloud and only in the central B59 core it rises to higher values, with three local peaks where it reaches values around unity. Centre and right: ¹³CO excitation temperature map in colour scale. This shows an increase of temperature towards the central B59 (zoomed in on the right panel). In all panels, the contours are the dust extinction as in Fig. 1. The darker contour at A_v = 10 which delineates the regions most likely to be in LTE.