All Figures

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{2931fig1.eps} \end{figure}$ Figure 1: CO (1-0) contour map of the Vela Molecular Cloud complex (Murphy & May 1991). The complex is composed of 4 clouds named A, B, C and D in the map. The positions of the observed sources are indicated and the filled circles are the location of the 50 other embedded young stellar objects. Indicated as well are the locations of the Vela Pulsar and the H II region 259, -4. The map is an adaptation of Fig. 1 of Liseau et al. (1992).
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{2931fig2.eps} \end{figure}$ Figure 2: Acquisition image in the stellar field of LLN 17 (IRAS 08448-4343. The orientation of the image ( $1024 \times 1024$ pixels) is North-South and the pixel scale is 1 $^{\prime \prime }$ /pixel and corresponds to the length of the arrow. The negative points are the result of the chopping. The main target is called the source IRS 17-57 in Massi et al. (1999) and the companion object is source IRS 17-40.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2931fig5.eps} \end{figure}$ Figure 5: The upper panel displays the water ice feature toward LLN 17. The adopted 2 Gaussian continuum, the 3.47 $\mu$ m feature and the methanol ice:water ice = 1:10 mixture are overplotted. The lower panel shows a zoom around the methanol feature. In this plot, the 2 Gaussian continuum has been subtracted.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{2931fig6.eps} \end{figure}$ Figure 6: The methanol feature toward LLN 17 is fitted by a single methanol mixture (CH₃OH:H₂O = 1:10) and by a 2 component mixture (70% CH₃OH:H₂O = 1:10 + 30% pure CH₃OH). The improvement with the 2 component mixture is marginal.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{2931fig7.eps} \end{figure}$ Figure 7: Normalized optical depths of the Vela sources fitted by a combination of 2 Gaussians, one centered at 3.01 $\mu$ m, the other one at 3.25 $\mu$ m. The upper panel shows the normalized optical depth for 3 Vela sources. The spectra are overplotted one on each other. The similarity between the 3 sources is so strong that it is difficult to separate the sources in the plot. The lower panel shows the spectrum of 2 other Vela sources. The spectra in both panels are fitted by a linear combination of two Gaussians.
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In the text

$\begin{figure} \par\includegraphics[width=8.1cm,clip]{2931fig8.eps} \end{figure}$ Figure 8: Optical depth at 3.25 $\mu$ m versus optical depth at 3.07 $\mu$ m. The straight lines can be fitted to the data. The origin of both lines is (0, 0). The data for sources which are not located in the Vela cloud are taken from the ISO-archive.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{2931fig11.ps} \end{figure}$ Figure 11: Continuum subtracted VLT ISAAC M-band spectrum of LLN 19 around the CO ice feature at 2140 cm^-1 (4.675 $\mu$ m). The spectrum is in an optical depth scale. The thick (red) line is the sum of the three fitting components.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{2931fig12.ps} \end{figure}$ Figure 12: The effects of the depolarization factor L on the water ice feature at 3300 cm^-1 ( $\sim$ 3.1 $\mu$ m). The effect of porosity for water ice at 120 K is shown (f=0 means compact ice while f=0.5 means that 50% of the volumn fraction is vacuum. The porous 120 K water ice absorption coefficient is close to the compact 40 K ice.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.4cm,clip]{2931fig13.ps} \end{figure}$ Figure 13: Water ice column density N(H₂O) versus the infrared luminosity $L_{{\rm IR}}$ . The error bars are 2 $\sigma$ level.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{2931fig14.eps} \end{figure}$ Figure 14: Water ice column density N(H₂O) normalized to the extinction $A_{{\rm V}}$ versus the ratio R(12/25). The error bars are 2 $\sigma$ level. The errors on the ratios R(12/25) are $\sim$ 5-10%. A trend is seen between N(H₂O)/ $A_{{\rm V}}$ and R(12/25).
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8.4cm,clip]{2931fig17.eps} \end{figure}$ Figure 17: Red component column density $N_{{\rm rc}}$ normalized to the extinction $A_{{\rm V}}$ versus the ratio R(12/25). The error bars are 2 $\sigma$ level. The errors on the ratios R(12/25) are $\sim$ 5-10%. A clear trend is seen between $N_{{\rm rc}}$ / $A_{{\rm V}}$ and R(12/25).
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8.4cm,clip]{2931fig18.eps} \end{figure}$ Figure 18: Total CO column density N(CO) and red component column density $N_{{\rm rc}}$ normalized to the extinction $A_{{\rm V}}$ versus N(H₂O)/ $A_{{\rm V}}$ in the left and right panel respectively. A clear trend is seen between N(CO) $_{{\rm rc}}$ / $A_{{\rm V}}$ and N(H₂O)/ $A_{{\rm V}}$ .
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{2931fig3.eps} \end{figure}$ Figure 3: Optical depth profiles of the 3 $\mu$ m ice feature for the 5 objects (dotted line) compared to ice coated grains at different radii using laboratory spectra taken from (Hudgins et al. 1993).
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{2931fig4.eps} \end{figure}$ Figure 4: L-band spectra of the companion objects. The water ice absorption feature is seen in all spectra. The spectra are dominated by the spurious features due to a bad telluric transmission correction. The dashed lines indicate the adopted continuum used to estimate the water-ice optical depth.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=14cm,clip]{2931fig9.ps} \end{figure}$ Figure 9: Best fit to the observed spectra using the three components phenomenological decomposition. The observed data points are plotted as open circles. The thick line is the sum of the three components after convolution by the profile of the ISAAC spectrometer ( $R\simeq 800$ ).
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=12cm,clip]{2931fig10.ps} \end{figure}$ Figure 10: Medium resolution spectra ( $R\simeq 10~000$ ) of three objects. The gas phase CO absorption lines are clearly visible and dominate the spectrum of LLN 19.
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In the text

$\begin{figure} \par\includegraphics[width=16.5cm,clip]{2931fig15.eps} \end{figure}$ Figure 15: Fit to the SED of LLN 13, LLN 17 and LLN 19. The upper panels show the fit to the entire SED while the upper panels focus on the near to mid-infrared range. Also shown are the contribution by the extincted central object, the dust scattered light and the dust thermal emission.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=17cm,clip]{2931fig16.eps} \end{figure}$ Figure 16: The upper left panel shows the infrared luminosity of the sources computed using the IRAS 4 bands fluxes versus an estimate of the extinction toward the objects. The radius of the circles at the position of each object is proportional to the observed abundance of CO ice. The upper right and lower left panels are two color-color diagrams. The infrared ratios R(12/25) and R(25/60) are ratios between the fluxes F(Jy) at 12 and 25 $\mu$ m and between fluxes at 25 and 60 $\mu$ m respectively. The lower right panel is a extinction versus R(12/25) diagram. The dashed-line represents a possible diving line between presence and absence of CO ice.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2931fig5.eps} \end{figure}$	Figure 5: The upper panel displays the water ice feature toward LLN 17. The adopted 2 Gaussian continuum, the 3.47 $\mu$ m feature and the methanol ice:water ice = 1:10 mixture are overplotted. The lower panel shows a zoom around the methanol feature. In this plot, the 2 Gaussian continuum has been subtracted.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{2931fig6.eps} \end{figure}$	Figure 6: The methanol feature toward LLN 17 is fitted by a single methanol mixture (CH₃OH:H₂O = 1:10) and by a 2 component mixture (70% CH₃OH:H₂O = 1:10 + 30% pure CH₃OH). The improvement with the 2 component mixture is marginal.
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$\begin{figure} \par\includegraphics[width=8.1cm,clip]{2931fig8.eps} \end{figure}$	Figure 8: Optical depth at 3.25 $\mu$ m versus optical depth at 3.07 $\mu$ m. The straight lines can be fitted to the data. The origin of both lines is (0, 0). The data for sources which are not located in the Vela cloud are taken from the ISO-archive.
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$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{2931fig11.ps} \end{figure}$	Figure 11: Continuum subtracted VLT ISAAC M-band spectrum of LLN 19 around the CO ice feature at 2140 cm^-1 (4.675 $\mu$ m). The spectrum is in an optical depth scale. The thick (red) line is the sum of the three fitting components.
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$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{2931fig12.ps} \end{figure}$	Figure 12: The effects of the depolarization factor L on the water ice feature at 3300 cm^-1 ( $\sim$ 3.1 $\mu$ m). The effect of porosity for water ice at 120 K is shown (f=0 means compact ice while f=0.5 means that 50% of the volumn fraction is vacuum. The porous 120 K water ice absorption coefficient is close to the compact 40 K ice.
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$\begin{figure} \par\includegraphics[angle=90,width=7.4cm,clip]{2931fig13.ps} \end{figure}$	Figure 13: Water ice column density N(H₂O) versus the infrared luminosity $L_{{\rm IR}}$ . The error bars are 2 $\sigma$ level.
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$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{2931fig14.eps} \end{figure}$	Figure 14: Water ice column density N(H₂O) normalized to the extinction $A_{{\rm V}}$ versus the ratio R(12/25). The error bars are 2 $\sigma$ level. The errors on the ratios R(12/25) are $\sim$ 5-10%. A trend is seen between N(H₂O)/ $A_{{\rm V}}$ and R(12/25).
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$\begin{figure} \par\includegraphics[angle=90,width=8.4cm,clip]{2931fig17.eps} \end{figure}$	Figure 17: Red component column density $N_{{\rm rc}}$ normalized to the extinction $A_{{\rm V}}$ versus the ratio R(12/25). The error bars are 2 $\sigma$ level. The errors on the ratios R(12/25) are $\sim$ 5-10%. A clear trend is seen between $N_{{\rm rc}}$ / $A_{{\rm V}}$ and R(12/25).
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$\begin{figure} \par\includegraphics[angle=90,width=8.4cm,clip]{2931fig18.eps} \end{figure}$	Figure 18: Total CO column density N(CO) and red component column density $N_{{\rm rc}}$ normalized to the extinction $A_{{\rm V}}$ versus N(H₂O)/ $A_{{\rm V}}$ in the left and right panel respectively. A clear trend is seen between N(CO) $_{{\rm rc}}$ / $A_{{\rm V}}$ and N(H₂O)/ $A_{{\rm V}}$ .
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$\begin{figure} \par\includegraphics[width=14cm,clip]{2931fig3.eps} \end{figure}$	Figure 3: Optical depth profiles of the 3 $\mu$ m ice feature for the 5 objects (dotted line) compared to ice coated grains at different radii using laboratory spectra taken from (Hudgins et al. 1993).
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$\begin{figure} \par\includegraphics[width=14cm,clip]{2931fig4.eps} \end{figure}$	Figure 4: L-band spectra of the companion objects. The water ice absorption feature is seen in all spectra. The spectra are dominated by the spurious features due to a bad telluric transmission correction. The dashed lines indicate the adopted continuum used to estimate the water-ice optical depth.
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$\begin{figure} \par\includegraphics[angle=90,width=14cm,clip]{2931fig9.ps} \end{figure}$	Figure 9: Best fit to the observed spectra using the three components phenomenological decomposition. The observed data points are plotted as open circles. The thick line is the sum of the three components after convolution by the profile of the ISAAC spectrometer ( $R\simeq 800$ ).
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$\begin{figure} \par\includegraphics[angle=90,width=12cm,clip]{2931fig10.ps} \end{figure}$	Figure 10: Medium resolution spectra ( $R\simeq 10~000$ ) of three objects. The gas phase CO absorption lines are clearly visible and dominate the spectrum of LLN 19.
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$\begin{figure} \par\includegraphics[width=16.5cm,clip]{2931fig15.eps} \end{figure}$	Figure 15: Fit to the SED of LLN 13, LLN 17 and LLN 19. The upper panels show the fit to the entire SED while the upper panels focus on the near to mid-infrared range. Also shown are the contribution by the extincted central object, the dust scattered light and the dust thermal emission.
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