All Figures

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f1.eps}}\end{figure}$ Figure 1: [J-H] versus H-[8] color diagram for $\sigma$ Ori cluster members with J< 14.4. Empty circles and squares are Class II/transitional disks and Class III objects respectively. Red filled circles show the location of our $\sigma$ Ori sample with Spitzer observations (32 objects in total). The histograms at the bottom show the distribution in H-[8] of all cluster members (empty) and of our sample (dashed), respectively. All Class II disks have H-[8] > 1.5.
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f2.eps}} \end{figure}$ Figure 2: Location of the $\sigma$ Ori targets on the HR diagram. Evolutionary tracks from D'Antona & Mazzitelli (1997), labeled with the stellar mass. Isochrones for 0.5, 1 and 5 Myr are shown by the dashed lines.
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In the text

$\begin{figure} \par\resizebox{16cm}{!}{\includegraphics[]{8971f3.eps}} \end{figure}$ Figure 3: Normalized observed spectra in the HeI and Pa $\gamma$ region. The dotted lines show the wavelengths of the two lines.
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In the text

$\begin{figure} \par\resizebox{16cm}{!}{\includegraphics[]{8971f4.eps}} \end{figure}$ Figure 4: Normalized observed spectra in the Pa $\beta$ region. The wavelength of Pa $\beta$ is shown by the dotted line.
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f5.eps}} \end{figure}$ Figure 5: Comparison of the accretion luminosity computed from Pa $\gamma$ and that computed from Pa $\beta$ for all objects with Pa $\gamma$ detection. Dots are actual measurements, arrow 3 $\sigma$ upper limits. The dotted lines show the locus of $L_{\rm acc}$ (Pa $\gamma$ ) = $L_{\rm acc}$ (Pab) and the $\pm$ 0.5 range.
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f6.eps}} \end{figure}$ Figure 6: Accretion luminosity as function of the stellar luminosity for the Class II objects. Dots are actual measurements, arrow 3 $\sigma$ upper limits. The dotted lines show the location of the $L_{\rm acc}$ / $L_\ast$ =1.0, 0.1 and 0.01 ratios, respectively.
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f7.eps}}\end{figure}$ Figure 7: Mass accretion rate as a function of $M_\ast$ for $\sigma$ Ori ( top) and $\rho$ Oph ( bottom; from Natta et al. 2006). Dots are actual measurements, arrows 3 $\sigma$ upper limits. The dotted line (same in both panels) shows the $\log{M_{\rm acc}} = -7.3 + 1.8\times \log{M_\star}$ locus, which we take as a fiducial line to define ``high accretors'' (see text).
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f8.eps}}\end{figure}$ Figure 8: HeI equivalent width as function of $L_{\rm acc}$ for Class II objects. Dots are objects with an actual measurements of $L_{\rm acc}$ , while arrows are upper limits. For clarity, we do not plot the objects with $L_{\rm acc}$ upper limits and non-detection of the He I line. For the two cases where we resolve the P-Cygni profile of the HeI line, we show (connected by a line) the corresponding unresolved equivalent width and the HeI activity index (sum of absolute values of absorption and emission equivalent widths; Edwards et al. 2006).
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f9.eps}}\end{figure}$ Figure 9: Distribution of simulated fraction of high accretors in samples extracted from a parent distribution ias measured in $\rho$ Oph. The dashed line shows the fraction of high accretors in $\rho$ Oph, the dot-dashed line that in $\sigma$ Ori.
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f10.eps}}\end{figure}$ Figure 10: $\dot M_{\rm acc}$ vs. $M_\ast$ for $\sigma$ Ori (dots and arrows; same as Fig. 7) and Tr37 (from Sicilia-Aguilar et al. 2006b). Squares shows value of $\dot M_{\rm acc}$ derived from U-band photometry, triangles at $\log\mbox{$\dot M_{\rm acc}$ }=-9$ $M_\odot$ /yr are objects with no U-band excess but broad H $\alpha$ , triangles at $\log\mbox{$\dot M_{\rm acc}$ }=-11$ are objects with no U-band excess and narrow H $\alpha$ . Note that for this group Sicilia-Aguilar et al. estimate $\log$ $\dot M_{\rm acc}$ <-12, we plot them at -11 for convenience.
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f2.eps}} \end{figure}$	Figure 2: Location of the $\sigma$ Ori targets on the HR diagram. Evolutionary tracks from D'Antona & Mazzitelli (1997), labeled with the stellar mass. Isochrones for 0.5, 1 and 5 Myr are shown by the dashed lines.
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$\begin{figure} \par\resizebox{16cm}{!}{\includegraphics[]{8971f3.eps}} \end{figure}$	Figure 3: Normalized observed spectra in the HeI and Pa $\gamma$ region. The dotted lines show the wavelengths of the two lines.
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$\begin{figure} \par\resizebox{16cm}{!}{\includegraphics[]{8971f4.eps}} \end{figure}$	Figure 4: Normalized observed spectra in the Pa $\beta$ region. The wavelength of Pa $\beta$ is shown by the dotted line.
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$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f5.eps}} \end{figure}$	Figure 5: Comparison of the accretion luminosity computed from Pa $\gamma$ and that computed from Pa $\beta$ for all objects with Pa $\gamma$ detection. Dots are actual measurements, arrow 3 $\sigma$ upper limits. The dotted lines show the locus of $L_{\rm acc}$ (Pa $\gamma$ ) = $L_{\rm acc}$ (Pab) and the $\pm$ 0.5 range.
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$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f6.eps}} \end{figure}$	Figure 6: Accretion luminosity as function of the stellar luminosity for the Class II objects. Dots are actual measurements, arrow 3 $\sigma$ upper limits. The dotted lines show the location of the $L_{\rm acc}$ / $L_\ast$ =1.0, 0.1 and 0.01 ratios, respectively.
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$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f7.eps}}\end{figure}$	Figure 7: Mass accretion rate as a function of $M_\ast$ for $\sigma$ Ori ( top) and $\rho$ Oph ( bottom; from Natta et al. 2006). Dots are actual measurements, arrows 3 $\sigma$ upper limits. The dotted line (same in both panels) shows the $\log{M_{\rm acc}} = -7.3 + 1.8\times \log{M_\star}$ locus, which we take as a fiducial line to define ``high accretors'' (see text).
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$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics[]{8971f9.eps}}\end{figure}$	Figure 9: Distribution of simulated fraction of high accretors in samples extracted from a parent distribution ias measured in $\rho$ Oph. The dashed line shows the fraction of high accretors in $\rho$ Oph, the dot-dashed line that in $\sigma$ Ori.
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