Steps toward interstellar silicate mineralogy

Fabian, D.; Henning, Th.; Jäger, Cornelia; Mutschke, H.; Dorschner, J.; Wehrhan, O.

doi:10.1051/0004-6361:20011196

Cited by 229 publications

(248 citation statements)

References 26 publications

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“…Figure 5 shows IR spectra of San Carlos Olivine measured for the Kyoto and Jena samples. The spectral features of the hand-milled sample are similar to that of the Kyoto sample , in which the sample was prepared by hand-milling, while that of the ball-milled sample is similar to that of the Jena sample (Fabian et al 2001), in which the sample was prepared by ball-milling. Consequently, it is highly probable that the difference in the spectra from different laboratories is due to differences in shape and lattice distortion of particles, caused by the different sample preparation methods: the Kyoto samples are irregular particles with less crystal lattice distortion, while the Jena samples are rounded particles with large lattice distortion.…”

Section: Difference In Spectra By Different Laboratoriesmentioning

confidence: 65%

“…The difference is about 0.05-0.1 μm for 10, 11.2, and 19.5 μm peaks, and about 0.5 μm for 23 and 33 μm peaks. They suggested that the particle shape of the Jena sample is more spherical than the Kyoto sample, because the peak positions for olivine particles with near-spherical shape are located at shorter wavelengths than those with elongated or flat ellipsoidal shapes, as pointed out by Fabian et al (2001).…”

Section: Introductionmentioning

confidence: 93%

“…The shape effect can be discussed by comparing the experimental results with those calculated. Fabian et al (2001) showed calculated IR spectra of spheres, and two continuous distributions of ellipsoids (CDEs) of forsterite and olivine (Fo 95 ). They considered the CDEs with random orientations, and the distributions are characterized either by equal probability of all shapes (CDE1; Bohren & Human, 1983), or by a weighting where nearspherical shapes are most probable (CDE2; Ossenkopf et al 1992).…”

Section: Shape Effect On Spectramentioning

confidence: 99%

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Shape and lattice distortion effects on infrared absorption spectra of olivine particles

Imai

Koike

Chihara

et al. 2009

A&A

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We prepared sub-micron olivine (Fo 92 ) particles of different shapes and different degrees of crystal lattice distortion, and studied both effects on the infrared absorption spectra experimentally. We found that the peak positions of the spectra shifted to short wavelength when the number fraction of spherical grains became large, consistent with spectral calculations using the continuous distributions of ellipsoids (CDE) model. We also found for the first time that the spectral features become broader by crystal lattice distortion. The peak intensities are affected by both effects. The peak intensity decreases with lattice distortion in general, but some peaks are largely affected by particle shape. The spectral difference of olivine measured in different laboratories can be explained by both the shape and lattice distortion effects through sample preparation methods. Broadening features in the infrared spectra of forsterite ejecta from comet Tempel 1 obtained in the Deep Impact mission, and forsterite crystals in circumstellar regions, suggest that forsterite crystals undergo lattice distortion.

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Section: Difference In Spectra By Different Laboratoriesmentioning

confidence: 65%

Section: Introductionmentioning

confidence: 93%

Section: Shape Effect On Spectramentioning

confidence: 99%

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Shape and lattice distortion effects on infrared absorption spectra of olivine particles

Imai

Koike

Chihara

et al. 2009

A&A

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“…The spectra of the two classes of particulates differ significantly, as discussed by Tamanai et al (2006bTamanai et al ( , 2009b. Correspondence with astronomically observed infrared dust emission bands has been found to be better in some cases for the roundish shapes, especially for the oxides in AGB star outflows (Tamanai et al 2009b; see also Posch et al 1999;and Fabian et al 2001a), but in other cases better for the irregular shapes, especially for forsterite (Tamanai et al 2006b; see also Molster et al 2002;Fabian et al 2001b). Particle shapes and spectra are shown in Fig.…”

Section: Experimental Spectramentioning

confidence: 78%

Laboratory-based grain-shape models for simulating dust infrared spectra

Mutschke¹,

Min

Tamanai³

2009

A&A

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Context. Analysis of thermal dust emission spectra for dust mineralogy and physical grain properties depends on comparison spectra, which are either laboratory-measured infrared extinction spectra or calculated extinction cross sections based on certain grain models. Often, the agreement between these two kinds of spectra, if available, is not yet satisfactory because of the strong influence of the grain morphology on the spectra. Aims. We investigate the ability of the statistical light-scattering model with a distribution of form factors (DFF) to reproduce measured infrared dust extinction spectra for particles that are small compared to the wavelength, i.e. in the size range of 1 μm and smaller. Methods. We take advantage of new experimental spectra measured for free particles dispersed in air with accompanying information on the grain morphology. For the calculations, we used DFFs that were derived for aggregates of spherical grains, as well as for compact grain shapes corresponding to Gaussian random spheres. In addition we used a fitting algorithm to obtain the best-fit DFFs for the various laboratory samples. In this way we can independently derive information on the shape of the grains from their infrared spectra. Results. With the DFF model, we achieve an adequate fit of the experimental IR spectra. The differences in the IR band profiles between the spectra of particulates with different grain shapes are simply reflected by different DFFs. Irregular particle shapes require a DFF similar to that of a Gaussian Random Sphere with σ = 0.3, whereas roundish grain shapes are best fitted with that of a fractal aggregate of D f = 2.4-1.8. The fitted DFFs generally reproduce the measured spectral shapes quite well. For anisotropic materials, different DFFs are needed for the different crystallographic axes. The implications of this finding are discussed. Conclusions. The use of this model could be a step forward toward more realistic comparison data in infrared spectral analysis of thermal dust emission spectra, provided that these spectra are dominated by emission from submicron grains.

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“…Mg/(Fe + Mg) > 0.9 (see e.g. Jäger et al 1998;Fabian et al 2001;Koike et al 2003). For amorphous silicates, i.e.…”

Section: Introductionmentioning

confidence: 98%

The shape and composition of interstellar silicate grains

Min

Waters

Koter

et al. 2006

A&A

196

225

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We investigate the composition and shape distribution of silicate dust grains in the interstellar medium. The effects of the amount of magnesium and iron in the silicate lattice are studied in detail. We fit the spectral shape of the interstellar 10 µm extinction feature as observed towards the galactic center using various particle shapes and dust materials. We use very irregularly shaped coated and non-coated porous Gaussian Random Field particles as well as a statistical approach to model shape effects. For the dust materials we use amorphous and crystalline silicates with various composition as well as silicon carbide (SiC). The results of our analysis of the 10 µm feature are used to compute the shape of the 20 µm silicate feature and to compare this with observations of this feature towards the galactic center. By using realistic particle shapes to fit the interstellar extinction spectrum we are, for the first time, able to derive the magnesium fraction in interstellar silicates. We find that the interstellar silicates are highly magnesium rich (Mg/(Fe + Mg) > 0.9) and that the stoichiometry lies between pyroxene and olivine type silicates (O/Si ≈ 3.5). This composition is not consistent with that of the glassy material found in GEMS in interplanetary dust particles indicating that the amorphous silicates found in the Solar system are, in general, not unprocessed remnants from the interstellar medium. Also, we find that a significant fraction of silicon carbide (∼3%) is present in the interstellar dust grains. We discuss the implications of our results for the formation and evolutionary history of cometary and circumstellar dust. We argue that the fact that crystalline silicates in cometary and circumstellar grains are almost purely magnesium silicates is a natural consequence of our findings that the amorphous silicates from which they were formed were already magnesium rich.

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Steps toward interstellar silicate mineralogy

Cited by 229 publications

References 26 publications

Shape and lattice distortion effects on infrared absorption spectra of olivine particles

Shape and lattice distortion effects on infrared absorption spectra of olivine particles

Laboratory-based grain-shape models for simulating dust infrared spectra

The shape and composition of interstellar silicate grains

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