Online Material
Table 4: Characteristics of the observations.
Table 5:
Signal-to-noise ratios for detections of crystalline silicate features,
amorphous silicate 10 
m feature and silica.
![\begin{figure}
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\end{figure}](img135.png)
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Figure 15:
Spitzer/IRS spectra of young stars in the Perseus cloud, in units of Jy. Gray areas correspond to 3- |
| Open with DEXTER | |
uncertainties as estimated in Sect. ![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f21.ps}
\end{figure}](img136.png)
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Figure 16: Same as Fig. 15 but for the Taurus star sample. |
| Open with DEXTER | |
![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f22.ps}
\end{figure}](img137.png)
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Figure 17: Same as Fig. 15 but for the Chamaleon star sample. |
| Open with DEXTER | |
![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f23.ps}
\end{figure}](img138.png)
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Figure 18: Spitzer/IRS spectra for the Chamaleon sample: continued. |
| Open with DEXTER | |
![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f24.ps}
\end{figure}](img139.png)
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Figure 19: Same as Fig. 15 but for the Lupus star sample. |
| Open with DEXTER | |
![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f25.ps}
\end{figure}](img140.png)
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Figure 20: Same as Fig. 15 but for the Ophiuchus star sample. |
| Open with DEXTER | |
![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f26.ps}
\end{figure}](img141.png)
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Figure 21: Spitzer/IRS spectra for the Ophiuchus sample: continued. |
| Open with DEXTER | |
![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f27.ps}
\end{figure}](img142.png)
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Figure 22: Same as Fig. 15 but for the Serpens star sample. |
| Open with DEXTER | |
![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f28.ps}
\end{figure}](img143.png){kind=small}
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Figure 23: Same as Fig. 15 but for the 3 isolated stars in our sample. |
| Open with DEXTER | |
![\begin{figure}
\par\includegraphics[width=18cm,clip]{12062f29.ps}
\end{figure}](img144.png)
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Figure 24: Same as Fig. 15 but for the 4 objects with spectra similar to C-rich and O-rich AGB stars. |
| Open with DEXTER | |