2018MNRAS.480.1507T

In order to investigate populations of massive stars in massive star clusters, we have constructed a near-infrared image set: narrow bands of 1.87 and 2.07 µm and the K_s standard band with miniTAO, a 1-m infrared telescope at Atacama. 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 µm for WN-type Wolf-Rayet stars, luminous blue variables and Ofpe stars, and also clear excess in 2.07 µm for WC-type Wolf-Rayet stars. Our detection in 1.87 µm agrees well with the 1.87-µm detection with the Hubble Space Telescope by Dong et al. The 1.87-µm excess of WN stars seems to have a clear correlation to the K_s magnitude. The correlation suggests that the 1.87-µm excess originates in recombination line emission of H and He, and the K_s magnitude includes free-free radiation. Moreover, the K_s magnitude of WN-late stars, excluding the component of the free-free emission, seems to have nearly a common K_s magnitude. However, the colour-colour diagrams also enable us to find the extinction for each star and thus to draw extinction maps. Furthermore, almost all Mira variables reported by Matsunaga et al. are detected in our images. By using the extinction maps, several tens of extremely red sources except for Mira variables are detected. These are considered to be possibly low-temperature (T < 1000 K) objects.