Infrared reflectivity spectroscopy of silicate glasses

Gervais, F.; Blin, Annie; Massiot, Dominique; Coutures, Jean-Pierre; Chopinet, Marie‐Hélène; Naudin, F.

doi:10.1016/s0022-3093(87)80280-6

Cited by 118 publications

(64 citation statements)

References 10 publications

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“…Compared with the pyroxene sample, the peak at 1076 cm −1 for enstatite exhibited no splitting, which is similar to the results reported by Jäger et al [37,38]. The band at 796 cm −1 can be ascribed to a frequency shift of the in-plane bending vibrations from amorphous SiO 2 [38]. The peak at 646 cm −1 shifted to a higher wavenumber (664 cm −1 ) for the enstatite sample compared with that for pyroxene is due to the iron in our pyroxene sample (EDX characterization) [19].…”

Section: Resultssupporting

confidence: 89%

“…The peak at 646 cm −1 corresponds to the bending vibration of Si−O bonds owing to the interaction with [15,36,37]. Compared with the pyroxene sample, the peak at 1076 cm −1 for enstatite exhibited no splitting, which is similar to the results reported by Jäger et al [37,38]. The band at 796 cm −1 can be ascribed to a frequency shift of the in-plane bending vibrations from amorphous SiO 2 [38].…”

Section: Resultssupporting

confidence: 85%

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Catalytic conversion of acetylene to polycyclic aromatic hydrocarbons over particles of pyroxene and alumina

Tian

Liu

Hammonds

et al. 2013

Phil. Trans. R. Soc. A.

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Polycyclic aromatic hydrocarbons (PAHs) are known to be present in many astrophysical objects and environments, but our understanding of their formation mechanism(s) is far from satisfactory. In this paper, we describe an investigation of the catalytic conversion reaction of acetylene gas to PAHs over pyroxene and alumina. Crystalline silicates such as pyroxenes (with general formula [Mg, Fe]SiO 3 ) and alumina (Al 2 O 3 ) are observed astrophysically through their infrared spectra and are likely to promote grain surface chemical reactions. In the experiments reported here, gas-phase PAHs were produced by the catalytic reaction of acetylene over crystalline silicates and alumina using a pulsed jet expansion technique and the gaseous products detected using time-of-flight mass spectrometry. In a separate experiment, the catalytic formation of PAHs from acetylene was further confirmed with acetylene gas at atmospheric pressure flowing continuously through a fixed-bed reactor. The gas effluent and carbonaceous compounds deposited on the catalysts were dissolved separately in dichloromethane and analysed using gas chromatography–mass spectrometry. Among the samples studied, alumina showed higher activity than the pyroxene-type grains for the acetylene reaction. It is proposed that formation of the PAHs relies on the Mg 2+ ions in the pyroxenes and Al 3+ ions in alumina, where these ions act as Lewis acid sites. X-ray diffraction, Fourier transform infrared and high-resolution transmission electron microscopy techniques were used to characterize the structure and physical properties of the pyroxene and alumina samples.

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Section: Resultssupporting

confidence: 89%

Section: Resultssupporting

confidence: 85%

Catalytic conversion of acetylene to polycyclic aromatic hydrocarbons over particles of pyroxene and alumina

Tian

Liu

Hammonds

et al. 2013

Phil. Trans. R. Soc. A.

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show abstract

“…Moreover, this feature is seen in many other ISO spectra of oxygen-rich AGB stars with low massloss rate, suggesting a more fundamental cause. Gervais et al (1987) studied the infrared properties of silicate glasses and concluded that calcium-bearing silicates have a characteristic band around 30 μm. From the work of Mutschke et al (1998), we retrieved the optical data for two Ca-silicates, which do indeed show a feature at 30 μm.…”

Section: Fit To the Residual Spectrummentioning

confidence: 99%

“…Unfortunately, we do not have aluminum-free calciumbearing silicates in our dataset of optical constants, so we cannot directly probe the impact of the aluminum content on the optical properties of Ca 2 Mg 0.5 Al 2 Si 1.5 O 7 . Gervais et al (1987) studied the influence of aluminum content on silicate emission features and found it to have a minor impact on the strongest ressonances. This suggests that the over-abundance of aluminum found by us may be spurious and that an equally good fit to the Al 2 O 3 -subtracted residual spectrum could be achieved with a silicate with a lower aluminum content.…”

Section: Aluminum and Calcium Abundancesmentioning

confidence: 99%

Dusty wind of W Hydrae

Khouri

Waters

Koter

et al. 2015

A&A

107

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Context. Low-and intermediate-mass stars go through a period of intense mass-loss at the end of their lives, during the asymptotic giant branch (AGB) phase. While on the AGB a significant part, or even most, of their initial mass is expelled in a stellar wind. This process controls the final stages of the evolution of these stars and contributes to the chemical evolution of galaxies. However, the wind-driving mechanism of AGB stars is not yet well understood, especially so for oxygen-rich sources. Characterizing both the present-day mass-loss rate and wind structure and the evolution of the mass-loss rate of such stars is paramount to advancing our understanding of this processes. Aims. We study the dusty wind of the oxygen-rich AGB star W Hya to understand its composition and structure and shed light on the mass-loss mechanism. Methods. We modelled the dust envelope of W Hya using an advanced radiative transfer code. We analysed our dust model in the light of a previously calculated gas-phase wind model and compared it with measurements available in the literature, such as infrared spectra, infrared images, and optical scattered light fractions. Results. We find that the dust spectrum of W Hya can partly be explained by a gravitationally bound dust shell that probably is responsible for most of the amorphous Al 2 O 3 emission. The composition of the large (∼0.3 μm) grains needed to explain the scattered light cannot be constrained, but probably is dominated by silicates. Silicate emission in the thermal infrared was found to originate from beyond 40 AU from the star. In our model, the silicates need to have substantial near-infrared opacities to be visible at such large distances. The increase in near-infrared opacity of the dust at these distances roughly coincides with a sudden increase in expansion velocity as deduced from the gas-phase CO lines. The dust envelope of W Hya probably contains an important amount of calcium but we were not able to obtain a dust model that reproduces the observed emission while respecting the limit set by the gas mass-loss rate. Finally, the recent mass loss of W Hya is confirmed to be highly variable and we identify a strong peak in the mass-loss rate that occurred about 3500 years ago and lasted for a few hundred years.

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“…For the sake of clarity, the curves have been successively shifted by 0.4. e.g. by Gervais et al (1987) leading to a combined band of a huge width. The incorporation of Mg into the silicate network can occur in two different ways, as network former (4-fold coordination) and/or as network modifier (6-fold coordination).…”

Section: Spectral Propertiesmentioning

confidence: 99%

Steps toward interstellar silicate mineralogy

Jäger¹,

Dorschner²,

Mutschke³

et al. 2003

A&A

294

292

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Abstract. Amorphous silicate particles are generally assumed to be the main dust component in the envelopes of oxygen-rich evolved stars and may be considered the precursors of the pure crystalline enstatite and forsterite particles detected by ISO. We present optical constants in the broad wavelength range 0.2-500 µm for a unique series of pure amorphous Mg-silicates (Mg/Si in the range 0.7-2.4). They have been prepared by the sol-gel process, a chemical technique based on the condensation of Mg-and Si-hydroxides in a liquid phase. The salient feature of these Mg-silicates is the very small content of Si-OH bonds in the silicate network, which considerably reduces the activation energy of crystallization and, thus, decreases the temperature threshold for crystallization as well as crystallization time. The astrophysical relevance of our sol-gel silicates is shown by a comparison of optically thin model spectra based on dust emissivities with ISO-SWS spectra of AGB stars and with 10 µm emission profiles of such stars obtained by ground-based spectroscopy. As paradigmatic cases of AGB spectra with respect to the appearance of the silicate bands, TY Dra (slender bands and deep trough between them) and R Cas (broad bands and widely filled-up trough) were used, for which ISO-SWS spectra are available. The dust emissivity derived from TY Dra can be excellently reproduced by the models, suggesting that the dust grains consist indeed of pure amorphous Mg-silicates. Satisfactory agreement was also found with the mean 10 µm profiles of some groups of AGB stars and supergiants. Spectra with strong dust emission in the silicate trough like R Cas require additional contributions by other dust components, probably oxides. A rough orientation on the spectral properties of such potential trough opacity contributors has been obtained by subtracting a pure silicate spectrum (TY Dra) from a spectrum with a nearly filled trough and a less pronounced 20 µm band (R Cas). In agreement with other amorphous silicates, the spectral index of the new silicate analogues amounts to −2.

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Infrared reflectivity spectroscopy of silicate glasses

Cited by 118 publications

References 10 publications

Catalytic conversion of acetylene to polycyclic aromatic hydrocarbons over particles of pyroxene and alumina

Catalytic conversion of acetylene to polycyclic aromatic hydrocarbons over particles of pyroxene and alumina

Dusty wind of W Hydrae

Steps toward interstellar silicate mineralogy

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