Hardness ratio distribution for all detected X-ray sources (small symbols) and for those with infrared or optical counterpart with a probability higher than 90% (big symbols). Grey are unidentified sources, coloured circles are active coronae with colour indicating their spectral type, blue filled squares are extragalactic objects, open squares highlight the pre-main sequence stars (T Tauri and HeAe), and filled red star are X-ray binaries (CVs and HMXBs). We limit to sources with HR errors smaller than 0.3 and with . The mean errors are plotted in the upper left corners. For comparison we show the expected hardness ratio values for a typical AGN (power law with photon index Γ = 1.9) and for 1020 < NH < 1023 cm-2, as a shaded area with a width equal to the mean HR2 and HR3 errors in the left and right panels respectively. Lines indicate the position of stars of different ages and main-sequence and evolved binaries (see legend in Fig. 12).
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