Cluster CCDs for regions A (left), B (middle), and the control field (right). We use the same symbols as in Fig. 4 to mark the spectroscopically observed stars. In the diagrams we mark with segmented lines the position of an O8 V (blue lines) and a K5 V star (red lines), following the Rieke extinction law (Rieke et al. 1989), as used in this work. Thicker black segmented lines show the expected position for T Tauri stars along the extinction vector. In the region B diagram, we show with red circles the stars with infrared excess, candidates to Herbig Ae/Be objects.