K versus H − K diagram of all sources with HK colours. Filled, black circles represent sources within r < 15.5″ with considerable IR-excesses (at λ > 2   μm). The small horizontal arrow points to the position of source B, with H − K = 5.39. Open black circles have JHK colours of reddened photospheres. Sources outside the cluster area are plotted as triangles; filled symbols (red) show infrared excesses and open (blue) symbols do not. For reference, the thick solid line marks the loci of the main-sequence (MS) stars from Koornneef (1983) for a distance of 2.5 kpc and reddened by E(H − K) = 0.2, corresponding to A_V = 4.2. The thin continuous line represents the ZAMS and 10⁵ yr isochrone (Palla & Stahler 1999) for a distance of 8.0 kpc and reddening of E(H − K) = 0.75 (A_V = 12.5), parameters that seem to fit the likely cluster members with no infrared excess. The short-dashed line defines the reddening vector from Rieke & Lebofsky (1985) and the long arrow marks the average slope of near-infrared excesses caused by discs around young stellar objects, as determined by Salas et al. (2006). A colour version of this figure is available in the electronic edition.