In this Letter we communicate optical data of Mg-Fe sulfides in the wavelength range from 10 to 500 micrometer. The sulfides were prepared in our laboratory in order to test the tentative identification of a prominent circumstellar emission band at 30 micrometer observed in carbon-rich Asymptotic Giant Branch (AGB) stars, protoplanetary, and planetary nebulae with Mg-S vibrations in sulfide grains. Arguments in favor of the existence of an interstellar sulfide dust component consisting of FeS or iron-rich Mg-Fe sulfides are discussed. Model calculations for the source IRC +10216 based on the communicated optical data demonstrate their practical use. The possibilities for the observational detection of interstellar FeS bands are considered.
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Begemann et al. (1994) studied this question.