2MASS (J − H) versus (H − K) diagram for the observed sources. Squares, asterisks, and stars represent objects in the three clumps, as indicated in the legend. The circles refer to the “non-clump” stars. The solid curve shows the relation between these indexes for main sequence stars (lower branch; Bessell & Brett 1988) and giants (upper branch; Kenyon & Hartmann 1995), where the 2MASS color trasformations were used. The A_V = 1 mag reddening vector is shown with an arrow. The typical 2MASS photometric errors are overplotted on the lower-left corner of the panel.