Top panel: J − K_s versus H − K_s diagram of the observed stars. Spectral-types are marked as shown in the figure legend; the two dashed curves indicate the reddening curves of naked M1 and O9 stars. Bottom panel: K_s− 8 versus H − K_s diagram; a reddening curve for an M1 star is shown with a dashed line. Star #22 (cLBV) shows infrared excess at 8 μm. The two foreground stars #1 (OBe) and #26 (B4-A4) have notable infrared excess. Star #7 was not plotted (8 μm confused).