Combined spectrum of 133P in the region of the CN band (left) and that of the “gas” (right), after the subtraction of the dust spectrum. The intensity scale is the same for both and the look up table is logarithmic. The spectral region is between 3500 and 4500 Å and the spatial region is from  − 15 000 to 15 000 km of projected nucleocentric distance (ρ). Notice that no emission bands are seen within the SNR. The region very close to the object photometric center is very noisy because the emission of the dust is strong, but a few thousands km farther the SNR improves.