Compositional dependence of infrared absorption spectra of crystalline silicate

Koike, C.; Chihara, H.; Tsuchiyama, A.; Shimada, Hiroshi; Sogawa, Hiromitsu; Okuda, H.

doi:10.1051/0004-6361:20021831

Cited by 160 publications

(254 citation statements)

References 15 publications

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“…Koike et al 2003). Even a small fraction of iron (x ∼ 0.05) leads to a band position at λ > 70 μm (see Fig.…”

Section: Effects Of Iron Contentmentioning

confidence: 92%

“…The 69 μm band is Influence of the iron cation fraction relative to magnesium in the olivine material on the peak wavelength of the 69 μm band. The data (black crosses) are from Koike et al (2003), taken at 295 K and the blue line is a linear fit.…”

Section: Effects Of Iron Contentmentioning

confidence: 99%

“…The green asterisks are taken from Koike et al (2003) and the blue crosses are based on Suto et al (2006), computed with the DHS model (Min et al 2003) and a grain size of 0.1 μm. The black arrow indicates the temperature dependency.…”

Section: Searching For the 69 μM Band In The Pacs Spectramentioning

confidence: 99%

“…Bowey et al 2002;Koike et al 2003;Suto et al 2006). Prior to the Herschel observations, the 69 μm band has only been detected by ISO in one protoplanetary disk (HD 100546, Malfait et al 1998).…”

Section: Introductionmentioning

confidence: 99%

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The 69μm forsterite band in spectra of protoplanetary disks. Results from theHerschelDIGIT programme

Sturm

Bouwman

Henning

et al. 2013

A&A

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Context. We have analysed far-infrared spectra of 32 circumstellar disks around Herbig Ae/Be and T Tauri stars obtained within the Herschel key programme Dust, Ice and Gas in Time (DIGIT). The spectra were taken with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory. In this paper we focus on the detection and analysis of the 69 μm emission band of the crystalline silicate forsterite. Aims. This work aims at providing an overview of the 69 μm forsterite bands present in the DIGIT sample. We use characteristics of the emission band (peak position and FWHM) to derive the dust temperature and to constrain the iron content of the crystalline silicates. With this information, constraints can be placed on the spatial distribution of the forsterite in the disk and the formation history of the crystalline grains. Methods. The 69 μm forsterite emission feature is analysed in terms of position and shape to derive the temperature and composition of the dust by comparison to laboratory spectra of that band. The PACS spectra are combined with existing Spitzer IRS spectra and we compare the presence and strength of the 69 μm band to the forsterite bands at shorter wavelengths. Results. A total of 32 disk sources have been observed. Out of these 32, 8 sources show a 69 μm emission feature that can be attributed to forsterite. With the exception of the T Tauri star AS 205, all of the detections are for disks associated with Herbig Ae/Be stars. Most of the forsterite grains that give rise to the 69 μm bands are found to be warm (∼100-200 K) and iron-poor (less than ∼2% iron). AB Aur is the only source where the emission cannot be fitted with iron-free forsterite requiring approximately 3-4% of iron. Conclusions. Our findings support the hypothesis that the forsterite grains form through an equilibrium condensation process at high temperatures. The large width of the emission band in some sources may indicate the presence of forsterite reservoirs at different temperatures. The connection between the strength of the 69 and 33 μm bands shows that at least part of the emission in these two bands originates fom the same dust grains. We further find that any model that can explain the PACS and the Spitzer IRS observations must take the effects of a wavelength dependent optical depth into account. We find weak indications of a correlation of the detection rate of the 69 μm band with the spectral type of the host stars in our sample. However, the sample size is too small to obtain a definitive result.

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“…Koike et al 2003). Even a small fraction of iron (x ∼ 0.05) leads to a band position at λ > 70 μm (see Fig.…”

Section: Effects Of Iron Contentmentioning

confidence: 92%

Section: Effects Of Iron Contentmentioning

confidence: 99%

Section: Searching For the 69 μM Band In The Pacs Spectramentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The 69μm forsterite band in spectra of protoplanetary disks. Results from theHerschelDIGIT programme

Sturm

Bouwman

Henning

et al. 2013

A&A

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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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