Properties of Star Clusters - I: Automatic Distance and Extinction
  Estimates
  Determining star cluster distances is essential to analyse their properties
and distribution in the Galaxy. In particular it is desirable to have a
reliable, purely photometric distance estimation method for large samples of
newly discovered cluster candidates e.g. from 2MASS, UKIDSS-GPS and VISTA-VVV.
Here, we establish an automatic method to estimate distances and reddening from
NIR photometry alone, without the use of isochrone fitting. We employ a
decontamination procedure of JHK photometry to determine the density of stars
foreground to clusters and a galactic model to estimate distances. We then
calibrate the method using clusters with known properties. This allows us to
establish distance estimates with better than 40% accuracy.
  We apply our method to determine the extinction and distance values to 378
known open clusters and 397 cluster candidates from the list of Froebrich,
Scholz and Raftery (2003). We find that the sample is biased towards clusters
of a distance of approximately 3kpc, with typical distances between 2 and 6kpc.
Using the cluster distances and extinction values, we investigate how the
average extinction per kiloparsec distance changes as a function of Galactic
longitude. We find a systematic dependence that can be approximated by
A_H(l)[mag/kpc]=0.10+0.001*|l-180deg|/deg for regions more than 60deg from the
Galactic Centre.
