Low-metallicity Young Clusters in the Outer Galaxy I. Sh 2-207
  To study star formation in low metallicity environments ([M/H] ~ -1 ,dex), we
obtained deep near-infrared (NIR) images of Sh 2-207 (S207), which is an HII
region in the outer Galaxy with spectroscopically determined metallicity of
[O/H] ~= -0.8 dex. We identified a young cluster in the western region of S207
with a limiting magnitude of Ks =19.0 mag (10 sigma) that corresponds to a mass
detection limit of <~0.1 M_sun and enables the comparison of star-forming
properties under low metallicity with those of the solar neighborhood. From the
fitting of the K-band luminosity function (KLF), the age and distance of S207
cluster are estimated at 2-3Myr and ~4 kpc, respectively. The estimated age is
consistent with the suggestion of small extinctions of stars in the cluster (Av
~ 3 mag) and the non-detection of molecular clouds. The reasonably good fit
between observed KLF and model KLF suggests that the underlying initial mass
function (IMF) of the cluster down to the detection limit is not significantly
different from the typical IMFs in the solar metallicity. From the fraction of
stars with NIR excesses, a low disk fraction (<10 %) in the cluster with
relatively young age is suggested, as we had previously proposed.
