Mid-Infrared Spectral Evolution of Amorphous Magnesium Silicate Smokes Annealed in Vacuum: Comparison to Cometary Spectra

Grain growth in the inner regions of Herbig Ae/Be star disks

“…The most natural explanation of this phenomenon is thermal annealing of amorphous grains in the inner parts of the disk, where temperatures above the crystallisation temperature of silicates (about 1000-1100 K, Hallenbeck et al 1998) can be reached. BO01 have analysed the 10 µm band composition and conclude that the presence of SiO 2 and forsterite indicate that thermal annealing produced the crystalline silicates.…”

Metastable Eutectic Condensation in a Mg‐Fe‐SiO‐H2‐O2Vapor: Analogs to Circumstellar Dust

“…Heterogeneous condensation of a magnesium-iron-silica vapor onto preexisting alumina surfaces should trap at least some of the iron that would then become incorporated into the crystalline silicate phases formed by annealing in the outÑow. Similarly, Hallenbeck, Nuth, & Daukantes (1998) and Hallenbeck, Nuth, & Nelson (2000) have demonstrated that amorphous magnesium silicate grains anneal on much more rapid timescales than do amorphous iron silicates. However, until the experiments reported in this paper, there had been no reason to postulate the existence of separate populations of iron-rich and magnesium-rich silicates in a typical AGB outÑow.…”

Structural processing of enstatite by ion bombardment

“…When the first ISO SWS (Infrared Space Observatory Short-Wavelength Spectrometer) spectra became available, one of the most surprising discoveries was the finding of clear evidence of the widespread presence of crystalline silicates in envelopes around evolved stars and also in Herbig Ae/Be stars (Waelkens et al 1996;Bouwman et al 2001). It can be assumed that a portion of the freshly condensed amorphous silicate particles (about 10-15%) are converted into the crystalline phase by thermal annealing within the circumstellar shell (Molster et al 1999;Hallenbeck et al 1998;Fabian et al 2000). Since the band positions of crystalline pyroxene and olivine are sensitive to the Mg/Fe ratio (Cameron & Papike 1982), the comparison between the spectral signature of synthetic and natural pyroxenes and olivines proves the presence of crystalline Mg-rich silicates that are responsible for the observed sharp MIR and FIR bands in the ISO spectra of circumstellar envelopes (Jäger et al 1998;Molster et al 2002a,b).…”