K-band spectra of the early-type star candidates (top) and RGB stars (bottom). Each star is identified above its spectrum with the ID assigned by Nishiyama & Schödel (2013) and Fig. 1. The position of the Br-γ, Na I doublet, Ca I triplet, four band heads of ¹²CO, and two band heads of ¹³CO are indicated by the vertical broken lines. The position and width of two narrow-band filters, 2.25 μm (NB2.25) and 2.34 μm (NB2.34), are also indicated by cyan hatched boxes. The spectra are sorted by the strength of the CO absorption feature at ≈2.294 μm from the top (weak) to the bottom (strong), in each panel.