The detection of iron sulfides in Planetary Nebulae

We present and discuss the detection, through mid IR spectroscopy, of iron sulfides in the carbon rich ejecta of evolved stars. We find the spectroscopic signature of iron sulfides at 23 μm. We also find weak features at ~34, 38 and 44 μm. The positions of these features correspond well with the resonances of the iron sulfide troilite. However, the relative strength of the 23 μm versus the other bands does not match the laboratory measurements, which suggests the presence of other iron sulfides besides troilite. The same broad feature around 23 μm has been found in young stellar objects. This detection may imply a carbon star origin for part of the iron sulfides found in meteorites and interplanetary dust particles.