All Figures

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F1.eps}}\end{figure}$ Figure 1: IR transmission spectra of magnesium silicates in the binary system MgO $\cdot$ SiO₂ for various MgO/SiO₂ ratios. The average particle size is less than 1 $\mu$ m. For the sake of clarity, the curves have been successively shifted by 0.4.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F2.eps}}\end{figure}$ Figure 2: Comparison between the calculated reflection spectra (solid lines) and the measured reflection spectra (dashed lines) demonstrated for two silicates.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F3.eps}}\end{figure}$ Figure 3: Optical constants of amorphous magnesium silicates of varying composition derived from reflection measurements by KKR and Lorentz oscillator fit methods. The n- and k-data files can be taken from the internet homepage of the Astrophysical Institute and University Observatory Jena (http://www.astro.uni-jena.de/Laboratory/Database/silicates.html).
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F4.eps}}\end{figure}$ Figure 4: Comparison of the optical data of Mg₂SiO₄ and MgSiO₃ produced by the sol-gel method with those of iron-containing proxene- and olivine glasses.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F5.eps}}\end{figure}$ Figure 5: Comparison of the optical constants of amorphous Mg₂SiO₄ produced by sol-gel method (solid line) and optical data of Mg₂SiO₄ films (dotted line) derived by Scott & Duley (1996).
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F6.eps}}\end{figure}$ Figure 6: Comparison of the absorption cross section of amorphous Mg₂SiO₄ produced by sol-gel method with that of Mg₂SiO₄ films calculated from the n and k data by Scott & Duley (1996). The solid lines stand for spherical particles, whereas the dotted lines represent the results for a continuous distribution of ellipsoids. The cross sections derived from our data have been offset by a factor of 10.
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In the text

$\begin{figure} \par\resizebox{8.45cm}{!}{\includegraphics[clip]{2749_F7.eps}}\end{figure}$ Figure 7: Powder transmission spectra of Mg₂SiO₄ (in KBr pellets) with varying Si-OH content. All the samples have been annealed for 1h. The spectra clearly show the correlation between crystallization and the appearance of the characteristic vibrational band of isolated Si-OH bonds located at 2.7 $\mu$ m. The spectra have been vertically offset.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F8.eps}}\end{figure}$ Figure 8: Comparison of our sol-gel-produced magnesium silicates with the observed ISO-SWS spectrum of TY Draconis. In the second line of the insert the full silicate formulae have been truncated in order to save space. The mixture of Mg_1.5SiO_3.5, Mg₂SiO₄, and Mg_2.4SiO_4.4 (for a CDE) gives the best reproduction of the dust emissivity reached so far.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F9.eps}}\end{figure}$ Figure 9: The effect of metallic iron impurities on the absorption efficiency $Q_{\rm abs}/a$ of amorphous MgSiO₄. The curves shown here have been calculated by considering the Fe inclusions as cores of core-mantle-particles.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F10.eps}}\end{figure}$ Figure 10: Reproduction of the mean spectra of AGB star groups A, B, C and supergiants group 1 (Speck et al. 2000) with sol-gel magnesium silicates of different stoichiometry. The solid lines represent the star spectra and the dashed or dotted lines stand for either single or mixtures of magnesium silicates. The AGB stars group C profile (lowest panel) equal portions of all magnesium silicates have been mixed.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F11.eps}}\end{figure}$ Figure 11: Difference between the normalized dust emissivities of R Cas and TY Dra. The broad maximum around 13 $\mu$ m is supposed to be caused by hitherto unidentified dust components which do not belong to the group of pure magnesium or magnesium-iron silicates.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F12.eps}}\end{figure}$ Figure 12: Calculated absorption cross sections per unit volume of the magnesium silicates for spheres (solid lines) and CDE (dashed lines).
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F1.eps}}\end{figure}$	Figure 1: IR transmission spectra of magnesium silicates in the binary system MgO $\cdot$ SiO₂ for various MgO/SiO₂ ratios. The average particle size is less than 1 $\mu$ m. For the sake of clarity, the curves have been successively shifted by 0.4.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F2.eps}}\end{figure}$	Figure 2: Comparison between the calculated reflection spectra (solid lines) and the measured reflection spectra (dashed lines) demonstrated for two silicates.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F3.eps}}\end{figure}$	Figure 3: Optical constants of amorphous magnesium silicates of varying composition derived from reflection measurements by KKR and Lorentz oscillator fit methods. The n- and k-data files can be taken from the internet homepage of the Astrophysical Institute and University Observatory Jena (http://www.astro.uni-jena.de/Laboratory/Database/silicates.html).
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F4.eps}}\end{figure}$	Figure 4: Comparison of the optical data of Mg₂SiO₄ and MgSiO₃ produced by the sol-gel method with those of iron-containing proxene- and olivine glasses.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F5.eps}}\end{figure}$	Figure 5: Comparison of the optical constants of amorphous Mg₂SiO₄ produced by sol-gel method (solid line) and optical data of Mg₂SiO₄ films (dotted line) derived by Scott & Duley (1996).
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$\begin{figure} \par\resizebox{8.45cm}{!}{\includegraphics[clip]{2749_F7.eps}}\end{figure}$	Figure 7: Powder transmission spectra of Mg₂SiO₄ (in KBr pellets) with varying Si-OH content. All the samples have been annealed for 1h. The spectra clearly show the correlation between crystallization and the appearance of the characteristic vibrational band of isolated Si-OH bonds located at 2.7 $\mu$ m. The spectra have been vertically offset.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F8.eps}}\end{figure}$	Figure 8: Comparison of our sol-gel-produced magnesium silicates with the observed ISO-SWS spectrum of TY Draconis. In the second line of the insert the full silicate formulae have been truncated in order to save space. The mixture of Mg_1.5SiO_3.5, Mg₂SiO₄, and Mg_2.4SiO_4.4 (for a CDE) gives the best reproduction of the dust emissivity reached so far.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F9.eps}}\end{figure}$	Figure 9: The effect of metallic iron impurities on the absorption efficiency $Q_{\rm abs}/a$ of amorphous MgSiO₄. The curves shown here have been calculated by considering the Fe inclusions as cores of core-mantle-particles.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F11.eps}}\end{figure}$	Figure 11: Difference between the normalized dust emissivities of R Cas and TY Dra. The broad maximum around 13 $\mu$ m is supposed to be caused by hitherto unidentified dust components which do not belong to the group of pure magnesium or magnesium-iron silicates.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[clip]{2749_F12.eps}}\end{figure}$	Figure 12: Calculated absorption cross sections per unit volume of the magnesium silicates for spheres (solid lines) and CDE (dashed lines).
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