Equivalent width map for the Na I D doublet (top) and the DIB ratio 5780/5797 (bottom). All selected cluster stars are colored in 31 groups according to their Voronoi-bin. The color reflects the measured total equivalent width of the Na I D doublet for each composite spectrum per bin with an average of about 960 mÅ. The center of the globular cluster is at coordinate origin and marked with a red star. Brightness contours of the globular cluster are shown as white lines. For the contour plot, the white light image was smoothed to a resolution of 20 arcsec.