CCD UBV photometry of the open cluster NGC 6819
  We present the results of CCD UBV observations of the open cluster NGC 6819.
We calculated the stellar density profile in the cluster's field to determine
the structural parameters of NGC 6819. Using the existing astrometric data, we
calculated the probabilities of the stars being physical members of the
cluster, and used these objects in the determination of the astrophysical
parameters of NGC 6819. We inferred the reddening and metallicity of the
cluster as $E(B-V)=0.130\pm0.035$ mag and $[Fe/H]=+0.051\pm 0.020$ dex,
respectively, using the U-B vs B-V two-colour diagram and UV excesses of the
F-G type main-sequence stars. We fit the colour-magnitude diagrams of NGC6819
with the PARSEC isochrones and derived the distance modula, distance and age of
the cluster as $\mu_{V}=12.22\pm 0.10$ mag, $d=2309\pm106$ pc and $t=2.4\pm0.2$
Gyr, respectively. The parameters of the galactic orbit estimated for NGC 6819
indicate that the cluster is orbiting in a slightly eccentric orbit of $e=0.06$
with a period of $P_{orb}=142$ Myr. The slope of the mass function estimated
for the cluster is close to the one found for the stars in the solar
neighbourhood.
