HST/NICMOS observations of the GLIMPSE9 stellar cluster
  We present HST/NICMOS photometry, and low-resolution K-band spectra of the
GLIMPSE9 stellar cluster. The newly obtained color-magnitude diagram shows a
cluster sequence with H-Ks =1 mag, indicating an interstellar extinction
Aks=1.6\pm0.2 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\pm0.4 kpc. Presuming that the population is coeval, we derive an age
between 15 and 27 Myr, and a total cluster mass of 1600\pm400 Msun, integrated
down to 1 Msun. In the vicinity of GLIMPSE9 are several HII regions and SNRs,
all of which (including GLIMPSE 9) 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.
