CCD UBVRI photometry of NGC 6811
  We present the results of CCD UBVRI observations of the open cluster NGC 6811
obtained on 18th July 2012 with the 1m telescope at the T\"UB\.ITAK National
Observatory (TUG). Using these photometric results, we determine the structural
and astrophysical parameters of the cluster. The mean photometric uncertainties
are better than 0.02 mag in the V magnitude and B-V, V-R, and V-I colour
indices to about 0.03 mag for U-B among stars brighter than magnitude V=18.
Cluster member stars were separated from the field stars using the Galaxia
model of Sharma et al. (2011) together with other techniques. The core radius
of the cluster is found to be $r_{c}$=3.60 arcmin. The astrophysical parameters
were determined simultaneously via Bayesian statistics using the
colour-magnitude diagrams V versus B-V, V versus V-I, V versus V-R, and V
versus R-I of the cluster. The resulting most likely parameters were further
confirmed using independent methods, removing any possible degeneracies. The
colour excess, distance modulus, metallicity and the age of the cluster are
determined simultaneously as E(B-V)=0.05$\pm$0.01 mag, $\mu=10.06\pm0.08$ mag,
[M/H]=-0.10$\pm$0.01 dex and t=1.00$\pm$0.05 Gyr, respectively. Distances of
five red clump stars which were found to be members of the cluster further
confirm our distance estimation.
