All Figures

$\begin{figure} \par\includegraphics[width=8.25cm,clip]{9999f1A.ps}\includegraphics[width=8.15cm,clip]{9999f1B.ps}\end{figure}$ Figure 1: Left: color-coded ACIS-I image of the 17' $\times$ 17' field in Trumpler 16 (see color version in the electronic edition). Kernel smoothing was applied to highlight point sources. Energy bands for the RGB image are [0.5:1.5], [1.5:2.2], and [2.2:8.0] keV for the red, green, and blue colors, respectively. Contour lines show the spatial distribution of the dark V-shaped dust lane. Right: ACIS-I image composed with a H $_\alpha$ image. This image clearly show the sharp cut, along the V-shape structure, in the spatial distribution of X-ray sources.
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{9999f2.ps}\end{figure}$ Figure 2: Quantile color-color diagram (QCCD). The energy scale in the top X-axis shows the median energy values (Q₅₀). The grid pattern represents the location of simulated spectra in the diagram (Hong et al. 2004). Note: filled circles and open boxes refer to X-ray sources with and without 2MASS counterparts (see next section), respectively. Small dots (red) correspond to sources with unreliable quantile values affected by poor photon statistics ( $\leq$ 10 photons).
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In the text

$\begin{figure} \par\includegraphics[width=8.25cm,clip]{9999f3.ps}\end{figure}$ Figure 3: JHK $_{\rm s}$ color-color diagram from high-quality 2MASS photometry. F ILLED CIRCLES and DOTS refer to X-ray detected and undetected 2MASS sources, respectively. A STERISKS show the source population with intrinsic $K_{\rm s}$ excess. Identified 2MASS source known as O- and early B-type stars are indicated by SQUARES. The main sequence is shown for reference. We also show the classical T Tauri stars (CTTS) locus of Meyer et al. (1997) and reddening vectors ( dashed lines) with length corresponding to $A_{\rm v}$ = 13 mag. Note: (i) the 2MASS photometry of $\eta$ Carinae is severely affected, with Phot.Qual. = ``DDD''; (ii) the peculiar position of the red box with $H-K_{\rm s}<$ -0.1 corresponds to the massive binary CPD-592628AB (SpT: O9.5V+B0.3V).
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In the text

$\begin{figure} \par\includegraphics[width=8.3cm,clip]{9999f4A.ps}\hspace*{3mm} \includegraphics[width=8.3cm,clip]{9999f4B.ps}\end{figure}$ Figure 4: CM diagrams of the Trumpler 16 region. Symbols as in Fig. 4. The two parallel curves indicate the expected cluster loci for the assumed distance and no reddening, and for the mean reddening $A_{\rm v}$ = 3.6 mag. Masses are indicated on the left side of the unreddened isochrone. Identified OB stars show $K_{\rm s}$ magnitudes below 11. Stars with $K_{\rm s}$ excess show typically $J-K_{\rm s}>1$ . Note: the limitation imposed by the 2MASS photometry ( $K_{\rm s}\sim$ 14.5 mag) corresponds to a mass limit of 1.1 $M_\odot$ . Labels near OB stars refer to Simbad names ( left) and respective Spectral types ( right). The fact that stars Tr16-244 (O4If) and HD 93129AB (WN6ha+O4f) appear above the 120 $M_\odot$ track does not mean that they are more massive, since their evolutionary stages cannot be compared with a MS isochrone. $\eta$ Carinae was discarded because of the bad 2MASS photometry (Phot.qual. = ``DDD'', see text). Sources labeled with numbers indicate stars (with masses above 12 $M_\odot$ ) probably surrounded by disks.
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In the text

$\begin{figure} \par\hspace*{1.5mm}\includegraphics[width=5.5cm,clip]{9999f5A.ps}... ...5D.ps}\hspace*{1.5mm} \includegraphics[width=5.5cm,clip]{9999f5C.ps}\end{figure}$ Figure 5: Light curves (in the 0.5-8.0 keV band) showing different variability scenarios occurring among our 77 variable sources. Bin size is 900 s. The source number is indicated in each panel. Upper panels show a flare-like behavior with very quick rises and decay phases of hours, while bottom panels are slowly modulated variability. A probable flare+modulation variability is occurring in the last panel.
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{9999f6.ps}\end{figure}$ Figure 6: X-ray light-curve of the massive binary (O3.5V((f))+O8V) HD 93205. This light curve shows: i- a uniform decay probably related to the orbital motion of the system, with changing absorption $N_{\rm H}$ of the colliding-wind region along the line of sight; plus ii- a probable short-term variability (see text).
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,angle=0]{9999f7A.ps}\includegraphics[width=8.5cm,angle=0]{9999f7B.ps}\end{figure}$ Figure 7: Left: the solid histogram shows the $N_{\rm H}$ ( $A_{\rm v}^{\rm xspec}$ ) distribution of 415 spectral fitted sources with 2MASS counterparts. The upper scale was converted using an $N_{\rm H}$ / $A_{\rm v}$ ratio of 1.6 $\times$ 10²¹. The thick dashed histogram shows the $A_{\rm v}^{\rm near-IR}$ mag distribution for all near-IR counterparts as was computed in Sect. 4. Both distributions peak at $A_{\rm v}^{\rm xspec}$ = 3.35 (1 $\sigma$ = 0.4) mag and $A_{\rm v}^{\rm near-IR}$ = 3.26 mag (1 $\sigma$ = 0.3 dex). The shadowed histogram shows the $N_{\rm H}$ distribution of 148 sources with no near-IR counterpart. Right: same as the left panel for plasma temperatures (kT) with, in addition, the distribution for ``flaring'' sources (black-filled histogram). The peak of the overal distribution is at $\sim$ 1.6 keV.
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In the text

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{9999f8.ps}\end{figure}$ Figure 8: The X-ray luminosity distribution for 592 low-mass stars computed from a single $L_{\rm x}$ count-rate conversion factor is shown as a solid line. The grey filled histogram shows the $L_{\rm x}$ distribution for 354 X-ray sources without near-IR counterpart. The 77 variable sources are shown with the black-filled histogram. Upper-right inset (Hot stars) shows the unabsorbed $L_{\rm x}$ from X-ray spectral fits (see Sect. 8). Error bars are 1 $\sigma$ Poisson errors.
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In the text

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{9999f9.ps}\end{figure}$ Figure 9: X-ray luminosity vs. stellar mass for stars in the near-IR sample with masses determined from the PMS models of Siess et al. (2000). Tr16 stars are plotted by open and filled circles, corresponding to $L_{\rm x}$ from CF and spectral fits, respectively. Crosses indicate Cyg OB2 sources (Albacete Colombo et al. 2007), while small boxes are ONC sources (Preibisch et al. 2005). The thick gray line shows the linear regression fit to the Tr16 low-mass (0.7-2.5 $M_\odot$ ) stars.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{9999f10.ps}\end{figure}$ Figure 10: Cumulative distributions of X-ray luminosities for Trumpler 16 low-mass stars with masses 1.5 $\leq$ $M/M_\odot$ $\leq$ 2.5 (thick solid line). Dotted and dashed lines represent the $L_{\rm x}$ cumulative distributions for ONC and CygOB2, respectively, in the same mass range.
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In the text

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{9999f11.ps}\end{figure}$ Figure 11: Log ( $L_{\rm x}$ / $L_{\rm bol}$ ) versus log ( $L_{\rm bol}$ ) relation for massive stars in Tr16. Open boxes refer to suspected single stars and filled circles to known binaries. Notes: i- because of flare-like variability (see Sect. 5.1) observed in Tr16-#5 (B1.5V) and Tr16-#11 (B1V), their X-ray emission is probably dominated by a unknown lowmass star companion. ii- The star Tr16-#22 (O8.5V+?) has the highest log ( $L_{\rm x}$ / $L_{\rm bol}$ ) ratio ( $\sim$ -5.56) among all MS OB-type stars of the region.
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{9999f6.ps}\end{figure}$	Figure 6: X-ray light-curve of the massive binary (O3.5V((f))+O8V) HD 93205. This light curve shows: i- a uniform decay probably related to the orbital motion of the system, with changing absorption $N_{\rm H}$ of the colliding-wind region along the line of sight; plus ii- a probable short-term variability (see text).
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{9999f10.ps}\end{figure}$	Figure 10: Cumulative distributions of X-ray luminosities for Trumpler 16 low-mass stars with masses 1.5 $\leq$ $M/M_\odot$ $\leq$ 2.5 (thick solid line). Dotted and dashed lines represent the $L_{\rm x}$ cumulative distributions for ONC and CygOB2, respectively, in the same mass range.
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