Dust and the spectral energy distribution of the OH/IR star OH   127.8+0.0: Evidence for circumstellar metallic iron
  We present a fit to the spectral energy distribution of OH 127.8+0.0, a typical asymptotic giant branch star with an optically thick circumstellar dust shell. The fit to the dust spectrum is achieved using non-spherical grains consisting of metallic iron, amorphous and crystalline silicates and water ice. Previous similar attempts have not resulted in a satisfactory fit to the observed spectral energy distributions, mainly because of an apparent lack of opacity in the 3--8 micron region of the spectrum. Non-spherical metallic iron grains provide an identification for the missing source of opacity in the near-infrared. Using the derived dust composition, we have calculated spectra for a range of mass-loss rates in order to perform a consistency check by comparison with other evolved stars. The L-[12 micron] colours of these models correctly predict the mass-loss rate of a sample of AGB stars, strengthening our conclusion that the metallic iron grains dominate the near-infrared flux. We discuss a formation mechanism for non-spherical metallic iron grains. 
F. Kemper (1), A. de Koter (1), L.B.F.M. Waters (1,2), J. Bouwman (1),   A.G.G.M. Tielens (3,4) ((1) University of Amsterdam...