SIMBAD references

We observed the reflection nebula NGC 7023 at various positions using wide and narrow band photometry centred on the 7.7 and 11.3µm PAH emission features and wide band photometry at 20 and 25µm. No significant variations have been detected over the nebula in the 7.3 and 20µm continuum relative to the total emission in the 6-15µm range (hereafter {GAMMA}). This result supports the hypothesis that most of the continuum emission in both bands come from very small grains. In contrast, the 7.7 and 11.3µm PAH emission features show clear variations. We find that in weaker radiation fields of the nebula the 11.3 and 7.7µm features are not the dominant emission components in the 6-15µm range. The 11.5µm band increases whereas the 11.3µm emission feature decreases relative to {GAMMA} in the outer parts of the nebula. The effect can be explained by increased hydrogenation of PAH molecules.