Some features of the Infra-Red Spectrum of NGC 7027 and an Estimate of its Sulphur Abundance

Observations of NGC 7027 in the range 10–12 µ are presented, with a spectral resolution of $$\Delta\lambda/\lambda = 0.005$$. The S IV line at 10.5 µ is clearly seen, and also the feature at 11.3 µ which has been observed by Gillet, Forrest & Merrill and which may be due to thermal emission from MgCO₃ grains. A previously unobserved sharp feature is seen at 11.9 µ. A sulphur abundance between 6.86 and 7.12 (relative to H = 12.00) is deduced from the intensity of the S IV line, and the possibility that the 11.3 and/or the 11.9 µ features are due to unresolved clusters of lines is briefly discussed.