Near-Infrared spectroscopy of the super star cluster in NGC1705
  We study the near-infrared properties of the super star cluster NGC1750-1 in
order to constrain its spatial extent, its stellar population and its age. We
use adaptive optics assisted integral field spectroscopy with SINFONI on the
VLT. We estimate the spatial extent of the cluster and extract its K-band
spectrum from which we constrain the age of the dominant stellar population.
Our observations have an angular resolution of about 0.11", providing an upper
limit on the cluster radius of 2.85+/-0.50 pc depending on the assumed
distance. The K-band spectrum is dominated by strong CO absorption bandheads
typical of red supergiants. Its spectral type is equivalent to a K4-5I star.
Using evolutionary tracks from the Geneva and Utrecht groups, we determine an
age of 12+/-6 Myr. The large uncertainty is rooted in the large difference
between the Geneva and Utrecht tracks in the red supergiants regime. The
absence of ionized gas lines in the K-band spectrum is consistent with the
absence of O and/or Wolf-Rayet stars in the cluster, as expected for the
estimated age.
