1.87 and 2.07um observations of 3 GC clusters

First, we observed the well-known three massive star clusters near the Galactic Centre. Colour-colour diagrams made from the set of images show clear excess in 1.87{mu}m for WN-type Wolf-Rayet stars, luminous blue variables and Ofpe stars, and also clear excess in 2.07{mu}m for WC-type Wolf-Rayet stars.

Our detection in 1.87{mu}m agrees well with the 1.87-{mu}m detection with the Hubble Space Telescope by Dong et al. The 1.87-{mu}m excess of WN stars seems to have a clear correlation to the Ks magnitude. The correlation suggests that the 1.87-{mu}m excess originates in recombination line emission of H and He, and the Ks magnitude includes free-free radiation. Moreover, the Ks magnitude of WN-late stars, excluding the component of the free-free emission, seems to have nearly a common Ks magnitude.