Star formation in the outer Galaxy: membership and fundamental
  parameters of the young open cluster NGC 1893
  Different environmental conditions can play a crucial role in determining
final products of the star formation process and in this context, less
favorable activities of star formation are expected in the external regions of
our Galaxy. We studied the properties of the young open cluster NGC 1893
located about 12 Kpc from the galactic center, to investigate how different
physical conditions can affect the process of star formation. By adopting a
multiwavelength approach, we compiled a catalog extending from X-rays to NIR
data to derive the cluster membership. In addition, optical and NIR photometric
properties are used to evaluate the cluster parameters. We find 415 diskless
candidate members plus 1061 young stellar objects with a circumstellar disk or
class II candidate members, 125 of which are also Halpha emitters. Considering
the diskless candidate members, we find that the cluster distance is
3.6$\pm$0.2 kpc and the mean interstellar reddening is E(B-V)=0.6$\pm$0.1 with
evidence of differential reddening in the whole surveyed region. NGC 1893
contains a conspicuous population of pre-main sequence stars together with the
well studied main sequence cluster population; we found a disk fraction of
about 70% similar to that found in clusters of similar age in the solar
neighbour and then, despite expected unfavorable conditions for star formation,
we conclude that very rich young clusters can form also in the outer regions of
our Galaxy.
