2010ApJ...708.1241M

We present Hubble Space Telescope/Near-Infrared Camera and Multi-Object Spectrometer photometry, and low-resolution K-band spectra of the GLIMPSE9 stellar cluster. The newly obtained color-magnitude diagram shows a cluster sequence with H - K_S= ∼1 mag, indicating an interstellar extinction A A^Ks_^ = 1.6±0.2 mag. The spectra of the three brightest stars show deep CO band heads, which indicate red supergiants with spectral type M1-M2. Two 09-B2 supergiants are also identified, which yield a spectrophotometric distance of 4.2±0.4 kpc. Presuming that the population is coeval, we derive an age between 15 and 27 Myr, and a total cluster mass of 1600±400 M_☉, integrated down to 1 M_☉. In the vicinity of GLIMPSE9 are several H II regions and supernova remnants, all of which (including GLIMPSE9) are probably associated with a giant molecular cloud (GMC) in the inner galaxy. GLIMPSE9 probably represents one episode of massive star formation in this GMC. We have identified several other candidate stellar clusters of the same complex.