On the Iron-rich Nature of Interstellar Silicate Dust

• 1、Geophysics College, Chengdu University of Technology, Chengdu 610000
• 2、Department of Physics and Astronomy, University of Missouri,, Columbia, MO 65211

Abstract：An accurate knowledge of the mineralogy (chemical composition and crystal structure of the silicate dust) in the interstellar medium is critical for understanding its origin and evolution. Crystalline silicates have been found in various astrophysical environments, including in dust shells around evolved starscomets, in debris disks around main-sequence stars, in protoplanetary disks around young pre-main sequence stars, and in comet comae. The upper limit of silicate crystallinity in the interstellar medium is estimated as~2-5%. Why is the crystalline silicate almost absent in the middel state of their evolution -- the diffuse interstellar medium (DISM)? The crystalline silicates are predominantly magnesium (Mg)-rich and iron (Fe)-poor or even Fe-free from their Infrared (IR) emission spectrum. The Fe content of crystalline silicates affects their ultraviolet (UV) and visual absorptivities. The purpose of this work is to check whether the weak absorptivies of Fe-poor crystalline silicate in UV and visual bands which can result in a lower equilibrium temperature and their sharp features can not be observed in the IR spectra. Our conclusion is that the interstellar dust in DISM has iron-rich nature and the crystallinity of silicates might not be underestimated in DISM.

Keywords： astrophysics diffuse interstellar medium interstellar dust silicate