All Figures

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{9325_f1.eps} \end{figure}$ Figure 1: The stars of our sample are plotted on this HR diagram. The evolutionary tracks between the pre-main sequence phase and the ZAMS are shown for the Ae/B9 stars. For this plot, we used the Palla & Stahler (1993) pre-main sequence tracks and the interpolation routines written by Testi et al. (1998). For the more massive Be stars, the pre-main sequence stage is less obvious due to the faster evolution of these stars, which makes them appear directly on the ZAMS.
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In the text

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{9325_f2.eps} \end{figure}$ Figure 2: O VI emission doublet near 1032 Å and 1038 Å in the FUSE spectrum of $\beta$ Pictoris observed in 2002. Here, only the exposures obtained during the night have been co-added, to avoid contamination by strong airglow emission lines due to the Earth's atmosphere. The positions of the H₂ transitions we should observe if H₂ was present along the line of sight are plotted. The H₂ levels are marked H20 for (v=0,J=0), H21 for (v=0,J=1), etc. For details on the C II absorption, see Roberge et al. (2006).
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In the text

$\begin{figure} \par\includegraphics[width=8.1cm,clip]{9325_f3.eps} \end{figure}$ Figure 3: Excitation diagram for H₂ towards AB Aurigæ. The observed level column densities (filled circles) show that H₂ is thermalized up to J=2 with a low kinetic temperature of about 56 K, while the column densities of the higher J-levels are consistent with a temperature of about 373 K. The populations of the first three energy levels are reproduced well by a PDR model (open square) with a low density of about 250 cm^-3 and a distance between the star and the gas of about 0.3 pc, with an excitation temperature of about 55 K. Our model does not reproduce the higher energy levels' excitation. This may be due to the presence of a second warm/hot gaseous component along our line of sight (see text).
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In the text

$\begin{figure} \par\includegraphics[width=8.1cm,clip]{9325_f4.eps} \end{figure}$ Figure 4: a) Excitation diagram of H₂ for HD 100546. The H₂ is thermalized up to J=4 with a kinetic temperature of 758 $\pm$ 147 K. The column densities of the higher J-levels are consistent with a temperature of about 1495 $\pm$ 70 K. b) Excitation diagram of H₂ for HD 163296. As for HD 100546, the H₂ is thermalized up to J=4 with a lower kinetic temperature of 432 $\pm$ 135 K. Here, only the v=0 levels up to J=4 are observed because of the later type of the star (A1Ve) and the low S/N ratio of the spectrum. c) Excitation diagram of H₂ for HD 104237. The H₂ is thermalized up to J=4 with a kinetic temperature of 306 $\pm$ 80 K. The higher J-levels may be consistent with a higher temperature, as suggested by the J=5 column density.
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In the text

$\begin{figure} \par\includegraphics[width=16cm,clip]{9325_f5.eps} \end{figure}$ Figure 5: Excitation diagram for H₂ towards the Be stars in our sample. For each star, the H₂ is thermalized up to $J \geq 3$ with a kinetic temperature of about $\sim$ 100 K.
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In the text

$\begin{figure} \par\includegraphics[width=16cm,clip]{9325_f6.eps} \end{figure}$ Figure 6: Best-fitting models obtained with the Meudon PDR Code overplotted on the excitation diagrams derived from the observed column densities (Fig. 5). The general shape of the diagrams are well-reproduced, but the excitation conditions of the higher J-levels cannot be reproduced well by the model (see text).
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In the text

$\begin{figure} \par\includegraphics[width=14.95cm,clip]{9325_f7.eps}\end{figure}$ Figure 7: Overplot of the FUSE spectrum of HD 76534 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). This plot only presents the portions of the spectrum where the stronger absorption lines of H₂ ( v=0, J=0, 1, 2) are observed. These principal prominent absorption troughs caused by molecular hydrogen are indicated throughout the spectrum. Airglow lines are indicated by $\oplus$ symbols.
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In the text

$\begin{figure} \par\includegraphics[width=7.9cm,clip]{9325_f13.eps} \end{figure}$ Figure 13: Total H₂ column densities as a function of the inclination angles away from edge-on of the CS disks given in Table 3.
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In the text

$\begin{figure} \par\includegraphics[width=7.9cm,clip]{9325_f14.eps} \end{figure}$ Figure 14: Total H₂ column densities as a function of the ages of those stars known to possess CS disks. Except for $\beta$ Pictoris and HD 135344, for which we cannot conclude because we only have upper limits, the amount of H₂ is greater towards the youngest stars. The correlation between the age and the amount of gas is shown by the dashed line.
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In the text

$\begin{figure} \par\includegraphics[width=7.9cm,clip]{9325_f15.eps} \end{figure}$ Figure 15: The total H₂ column densities as a function of the ages of the Be stars of our sample, which present no evidence of CS disks.
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In the text

$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f8.eps}\end{figure}$ Figure 8: Overplot of the FUSE spectrum of HD 176386 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). This plot only presents the portions of the spectrum where the stronger absorption lines of H₂ ( v=0, J=0, 1, 2) are observed. These principal prominent absorption troughs caused by molecular hydrogen are indicated throughout the spectrum. Airglow lines are indicated by $\oplus$ symbols.
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In the text

$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f9.eps}\end{figure}$ Figure 9: Overplot of the FUSE spectrum of HD 250550 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). Same legend as for Fig. 8. Here, the photospheric model does not fit the data well because of the strong stellar wind lines (for details see Bouret et al. 2003).
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In the text

$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f10.eps}\end{figure}$ Figure 10: Overplot of the FUSE spectrum of HD 85567 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). Same legend as for Fig. 8.
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In the text

$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f11.eps}\end{figure}$ Figure 11: Overplot of the FUSE spectrum of HD 259431 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). Same legend as for Fig. 8.
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In the text

$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f12.eps}\end{figure}$ Figure 12: Overplot of the FUSE spectrum of HD 38087 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). Same legend as for Fig. 8.
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In the text

$\begin{figure} \par\includegraphics[width=16cm,clip]{9325_f5.eps} \end{figure}$	Figure 5: Excitation diagram for H₂ towards the Be stars in our sample. For each star, the H₂ is thermalized up to $J \geq 3$ with a kinetic temperature of about $\sim$ 100 K.
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$\begin{figure} \par\includegraphics[width=16cm,clip]{9325_f6.eps} \end{figure}$	Figure 6: Best-fitting models obtained with the Meudon PDR Code overplotted on the excitation diagrams derived from the observed column densities (Fig. 5). The general shape of the diagrams are well-reproduced, but the excitation conditions of the higher J-levels cannot be reproduced well by the model (see text).
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$\begin{figure} \par\includegraphics[width=7.9cm,clip]{9325_f13.eps} \end{figure}$	Figure 13: Total H₂ column densities as a function of the inclination angles away from edge-on of the CS disks given in Table 3.
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$\begin{figure} \par\includegraphics[width=7.9cm,clip]{9325_f14.eps} \end{figure}$	Figure 14: Total H₂ column densities as a function of the ages of those stars known to possess CS disks. Except for $\beta$ Pictoris and HD 135344, for which we cannot conclude because we only have upper limits, the amount of H₂ is greater towards the youngest stars. The correlation between the age and the amount of gas is shown by the dashed line.
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$\begin{figure} \par\includegraphics[width=7.9cm,clip]{9325_f15.eps} \end{figure}$	Figure 15: The total H₂ column densities as a function of the ages of the Be stars of our sample, which present no evidence of CS disks.
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$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f9.eps}\end{figure}$	Figure 9: Overplot of the FUSE spectrum of HD 250550 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). Same legend as for Fig. 8. Here, the photospheric model does not fit the data well because of the strong stellar wind lines (for details see Bouret et al. 2003).
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$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f10.eps}\end{figure}$	Figure 10: Overplot of the FUSE spectrum of HD 85567 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). Same legend as for Fig. 8.
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$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f11.eps}\end{figure}$	Figure 11: Overplot of the FUSE spectrum of HD 259431 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). Same legend as for Fig. 8.
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$\begin{figure} \par\includegraphics[width=9.9cm,clip]{9325_f12.eps}\end{figure}$	Figure 12: Overplot of the FUSE spectrum of HD 38087 (thin line) and the synthetic spectrum obtained by combining our photospheric model with the results of the Meudon PDR Code (thick line). Same legend as for Fig. 8.
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