JHK color–color diagram for 977 stars with K < 15 mag. Nonvariable sources with combined errors <0.15 mag are shown in gray, the 136 variable sources with complete JHK data sets have colored symbols. The color codes for the K-variability are the following: amplitudes ≤0.2 mag red, ≤0.5 mag yellow, ≤1 mag green, and >1 mag magenta. The curve denotes the main sequence from M4 to B0 (Ducati et al. 2001), the dashed lines correspond to reddening paths for A_V = 30 mag, and the dotted line marks the limit for K-excess sources.