Volume 565, May 2014
|Number of page(s)||4|
|Published online||23 May 2014|
A hidden reservoir of Fe/FeS in interstellar silicates?
Institut d’Astrophysique Spatiale (IAS), Université Paris-Sud & CNRS, Bât. 121, 91405 Orsay, France
Received: 14 April 2014
Accepted: 8 May 2014
Context. The depletion of iron and sulphur into dust in the interstellar medium and the exact nature of interstellar amorphous silicate grains is still an open question.
Aims. We study the incorporation of iron and sulphur into amorphous silicates of olivine- and pyroxene-types and their effects on the dust spectroscopy and thermal emission.
Methods. We used the Maxwell-Garnett effective-medium theory to construct the optical constants for a mixture of silicates, metallic iron, and iron sulphide. We also studied the effects of iron and iron sulphide in aggregate grains.
Results. Iron sulphide inclusions within amorphous silicates that contain iron metal inclusions show no strong differences in the optical properties of the grains. A mix of amorphous olivine- and pyroxene-type silicate broadens the silicate features. An amorphous carbon mantle with a thickness of 10 nm on the silicate grains leads to an increase in absorption on the short-wavelength side of the 10 μm silicate band.
Conclusions. The assumption of amorphous olivine-type and pyroxene-type silicates and a 10 nm thick amorphous carbon mantle better matches the interstellar silicate band profiles. Including iron nano-particles leads to an increase in the mid-IR extinction, while up to 5 ppm of sulphur can be incorporated as Fe/FeS nano inclusions into silicate grains without leaving a significant trace of its presence.
Key words: dust, extinction / ISM: abundances
© ESO, 2014
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.