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Published online by Cambridge University Press: 07 August 2017
An unidentified emission feature at 21 μm has been detected in the IRAS Low Resolution Spectra (LRS) of 5 IRAS sources (Kwok, Volk, and Hrivnak 1989, Hrivnak and Kwok 1991). The sources are generally found to be F and G supergiants with cool, detached dust shells. We have searched for additional 21 μm sources in the LRS database and have obtained ground-based UKIRT spectra at 10 and 20 μm in an attempt to confirm the LRS feature.