All Figures

$\begin{figure} \par\includegraphics[width=17cm,height=16cm,clip]{6500fig1.ps} \end{figure}$ Figure 1: IRAS 100 $\mu$ m dust emission map of the Cha II dark cloud. The contours, from 10 to 40 MJy $\times$ sr^-1 in steps of 2.5 MJy $\times$ sr^-1, are also drawn (white lines). The big polygons define the area covered by the seven ESO2.2m+WFI pointings. The confirmed members of the cloud and the candidates selected in previous surveys are represented with open circles and squares, respectively; the black dots mark the objects recovered by our selection criteria (see Sect. 4).
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=14cm,height=24cm]{6500fig2.ps}} \end{figure}$ Figure 2: Photometric errors versus magnitudes and relative exponential fits for all the point-like sources detected in Cha II and for all the available filters. The "double sequence'', clearly visible in R and H $\alpha _{12}$ bands, is due to different seeing conditions in the individual exposures.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=13cm,height=8cm]{6500fig3.ps}} \end{figure}$ Figure 3: Completeness plots for extraction of artificial stars from the ChaII_2 mosaic (see Table 1) for all the photometric bands used in this work (see text).
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=8cm,height=6.5cm]{6500fig4.ps}} \end{figure}$ Figure 4: Theoretical R_C vs. (R-I)_C diagram. The isochrones (continuous curves) and PMS tracks (dashed curves), shifted to the distance modulus of Cha II (6.25 mag, Whittet et al. 1997) are in the WFI-Cousins photometric system. The dashed straight line represents the 95% completeness limit. The $A_{\rm V}=2$ mag reddening vector is shown.
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In the text

$\begin{figure} \par\resizebox{8.6cm}{!}{\includegraphics[width=2.5cm,height=1.5cm]{6500fig5.ps}} \end{figure}$ Figure 5: The ( m₈₅₆-m₉₁₄) index versus effective temperature relation derived from the corresponding WFI intermediate-band filters and the synthetic low-resolution StarDusty spectra for low-mass stars and BDs by Allard et al. (2000). The two solid curves show the relation for $\log g=5.0$ (lower boundary) and $\log g=3.5$ (upper boundary); the dashed curve represents the $T_{\rm eff}$ -colour relation for $\log g=4.0$ . The straight line is the empirical relationship derived by López-Martí et al. (2004).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,height=8cm,clip]{6500fig6.ps} \end{figure}$ Figure 6: Calibration relation between the ( $\rm H\alpha _{12}-H\alpha _7$ ) index and the H $\alpha$ equivalent width derived from the corresponding WFI intermediate-band filters and the synthetic low-resolution StarDusty spectra for low-mass stars and BDs by Allard et al. (2000).
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In the text

$\begin{figure} \par\includegraphics[width=7cm,height=7cm]{6500fig7.ps} \end{figure}$ Figure 7: ( $\rm H\alpha _{12}-H\alpha _7$ ) observed colours for PMS stars in L1616 as a function of the synthetic ( $\rm H\alpha_{12}~-~H\alpha_{7}$ ) colours (see text). The continuous line represents the best fit of the data; the dashed line has the offset a=0 and slope b=1.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,height=6.7cm,clip]{6500fig8.ps} \end{figure}$ Figure 8: Comparison between the H $\alpha$ equivalent width estimated in this work from the ( $\rm H\alpha _{12}-H\alpha _7$ ) photometric index and the one measured by Hughes & Hartigan (1992) and Barrado y Navascués & Jayawardhana (2004) for confirmed PMS stars in Cha II (open circles). The smaller black dots mark the objects recovered by our selection criteria (see Sect. 4).
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=2.3cm,height=1.6c... ...8.8cm}{!}{\includegraphics[width=2.3cm,height=1.6cm]{6500fig9b.ps}} \end{figure}$ Figure 9: I_C vs. (I_C-z) and I_C vs. (R-I)_C diagrams for the point-like objects in our survey (small gray dots). The lines represent the theoretical isochrones derived as explained in Sect. 3.1, shifted to the distance modulus of Cha II (6.25 mag, Whittet et al. 1997). The continuous line in each diagram represents the saturation limit. The big black dots represent the 37 sources selected from our criteria, while the open circles and squares represent the known PMS stars and candidates selected from previous surveys, respectively. The magnitudes reported by Hughes & Hartigan (1992) were used to plot the objects above and/or close to our saturation limits in any of the three broad-bands. The $A_{\rm V}=2$ mag reddening vector is shown in both diagrams.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=3cm,height=2.5cm]{6500fig10.ps}} \end{figure}$ Figure 10: (J-H) vs. (H-K) diagram for the sources detected in Cha II (small gray dots). The solid curve shows the relation between these indexes for main sequence stars (lower branch) and giants (upper branch). The dashed line indicates the classical T Tauri stars locus by Meyer et al. (1997). The continuous line is the dividing line between giants and dwarfs. The shaded area indicates the locus presumably uncontaminated by giants. The previously known PMS stars and candidates are indicated with open circles and squares respectively. The big black dots represent the objects selected in this work. The $A_{\rm V}=2$ mag reddening vector is shown. The two PMS stars which fall outside the selection area are the heavily veiled star Sz 47 (below the shaded area) and the binary Sz 60E (above the shaded area).
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=2.5cm,height=2.2cm]{6500fig11.ps}} \end{figure}$ Figure 11: R_C magnitudes versus ( $\rm H\alpha _{12}-H\alpha _7$ ) colours for the point-like objects in Cha II (small gray dots). The previously known PMS stars and candidates are indicated by open circles and squares, respectively, whereas the sources selected in this work are represented with big black dots. The $A_{\rm V}=2$ mag reddening vector is shown.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,height=17cm,clip]{6500fig12.ps} \end{figure}$ Figure 12: Spectral energy distributions of the 10 new candidates selected in this work. Dereddened optical data are represented with filled circles; the IR data are from 2MASS (filled squares), IRAC@Spitzer and MIPS@Spitzer (filled triangles and upside down triangles, respectively). The open circles represent the observed fluxes. The best-fitting StarDusty spectra by Allard et al. (2000) with the same temperature as the objects are over-plotted (see Sect. 5.3.2). WFI J12585611-7630105, WFI J13014752-7631023, and WFI J13031616-7629381 fall outside the areas mapped with MIPS and IRAC; although WFI J13071960-7655476 and WFI J13005297-7709478 fall in the area surveyed with MIPS, they were not detected.
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In the text

$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics[width=3cm,height=2.8cm]{6500fig13.ps}} \end{figure}$ Figure 13: Upper panel: comparison between the effective temperature resulting from the SED fitting procedure described in Sect. 5.3.2 and that derived from the spectral classification for the confirmed T Tauri stars in Cha II reported by Hughes & Hartigan (1992) and, for C 41, by Barrado y Navascués & Jayawardhana (2004) (open circles). The black dots mark the objects recovered by our selection criteria. The point at $T_{\rm spec}\approx 2900$ K represents ISO-CHA II 13 as reported by Alcalá et al. (2006). Lower Panel: comparison between the effective temperature resulting from the SED fitting procedure described in Sect. 5.3.2 and that derived from the $T_{\rm eff}$ vs. ( m₈₅₆-m₉₁₄) calibration. The open circles and squares represent previously known PMS stars and candidates, respectively. The black dots mark the objects recovered by our selection criteria.
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In the text

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics[width=2.3cm,height=1.6cm]{6500fig14.ps}} \end{figure}$ Figure 14: I_C vs. (R-I)_C and (J-H) vs. (H-K) diagrams for the PMS populations in Taurus and IC348. The isochrones, shifted by the corresponding distance modulus, are as in Fig. 9. The selection limits in the (J-H) vs. (H-K) diagrams are as in Fig. 10.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=8.5cm,height=6.5cm]{6500figA1.ps}} \end{figure}$ Figure A.1: Observed (dots) and dereddened (open triangles) spectral energy distribution of SA 98 653 normalised to the flux at 5556 Å. The best fitting model by Kurucz (1979) is over-plotted (continuous line).

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=12cm,height=13cm]{6500figB1.ps}} \end{figure}$ Figure B.1: The R, I, z (upper panel), $\rm H\alpha _7$ , $\rm H\alpha _{12}$ (central panel), 856 and 914 nm (lower panel) WFI+ESO2.2m transmission bands. Examples of two normalised NextGen spectra (Hauschildt et al. 1999) with $T_{\rm eff}=2500$ K and $T_{\rm eff}=6000$ K are over-plotted.

In the text

$\begin{figure} \par\includegraphics[width=7cm,height=9cm,clip]{6500figB2.ps} \end{figure}$ Figure B.2: The Cousins colours as a function of the WFI instrumental colours for the standard stars in the Landolt's field SA 98. The continuous lines display the best fit of the data while the dashed lines have slope equal to 1 (i.e. no correction).

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=8.5cm,height=6.5cm]{6500figB3.ps}} \end{figure}$ Figure B.3: Theoretical isochrones by Baraffe et al. (1998) and Chabrier et al. (2000) for the Cousins photometric system of Bessel (continuous line) and for the WFI-Cousins system (dashed lines, this work). In the smaller panel the 5 Myr isochrone by Chabrier et al. (2000) (continuous line) is compared with that reproduced by our algorithm when using the same Bessel filters (dashed line).

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=14cm,height=24cm]{6500fig2.ps}} \end{figure}$	Figure 2: Photometric errors versus magnitudes and relative exponential fits for all the point-like sources detected in Cha II and for all the available filters. The "double sequence'', clearly visible in R and H $\alpha _{12}$ bands, is due to different seeing conditions in the individual exposures.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=13cm,height=8cm]{6500fig3.ps}} \end{figure}$	Figure 3: Completeness plots for extraction of artificial stars from the ChaII_2 mosaic (see Table 1) for all the photometric bands used in this work (see text).
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=8cm,height=6.5cm]{6500fig4.ps}} \end{figure}$	Figure 4: Theoretical R_C vs. (R-I)_C diagram. The isochrones (continuous curves) and PMS tracks (dashed curves), shifted to the distance modulus of Cha II (6.25 mag, Whittet et al. 1997) are in the WFI-Cousins photometric system. The dashed straight line represents the 95% completeness limit. The $A_{\rm V}=2$ mag reddening vector is shown.
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$\begin{figure} \par\includegraphics[width=8cm,height=8cm,clip]{6500fig6.ps} \end{figure}$	Figure 6: Calibration relation between the ( $\rm H\alpha _{12}-H\alpha _7$ ) index and the H $\alpha$ equivalent width derived from the corresponding WFI intermediate-band filters and the synthetic low-resolution StarDusty spectra for low-mass stars and BDs by Allard et al. (2000).
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$\begin{figure} \par\includegraphics[width=7cm,height=7cm]{6500fig7.ps} \end{figure}$	Figure 7: ( $\rm H\alpha _{12}-H\alpha _7$ ) observed colours for PMS stars in L1616 as a function of the synthetic ( $\rm H\alpha_{12}~-~H\alpha_{7}$ ) colours (see text). The continuous line represents the best fit of the data; the dashed line has the offset a=0 and slope b=1.
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$\begin{figure} \par\includegraphics[width=8.6cm,height=6.7cm,clip]{6500fig8.ps} \end{figure}$	Figure 8: Comparison between the H $\alpha$ equivalent width estimated in this work from the ( $\rm H\alpha _{12}-H\alpha _7$ ) photometric index and the one measured by Hughes & Hartigan (1992) and Barrado y Navascués & Jayawardhana (2004) for confirmed PMS stars in Cha II (open circles). The smaller black dots mark the objects recovered by our selection criteria (see Sect. 4).
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[width=2.5cm,height=2.2cm]{6500fig11.ps}} \end{figure}$	Figure 11: R_C magnitudes versus ( $\rm H\alpha _{12}-H\alpha _7$ ) colours for the point-like objects in Cha II (small gray dots). The previously known PMS stars and candidates are indicated by open circles and squares, respectively, whereas the sources selected in this work are represented with big black dots. The $A_{\rm V}=2$ mag reddening vector is shown.
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$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics[width=2.3cm,height=1.6cm]{6500fig14.ps}} \end{figure}$	Figure 14: I_C vs. (R-I)_C and (J-H) vs. (H-K) diagrams for the PMS populations in Taurus and IC348. The isochrones, shifted by the corresponding distance modulus, are as in Fig. 9. The selection limits in the (J-H) vs. (H-K) diagrams are as in Fig. 10.
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