ASTROPHYSICS AND SPACE SCIENCE, vol.361, 2016 (SCI-Expanded)
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 +/- 0.035 mag and [Fe/H] = +0.051 +/- 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 NGC 6819 with the PARSEC isochrones and derived the distance modula, distance and age of the cluster as mu(V) = 12.22 +/- 0.10 mag, d = 2309 +/- 106 pc and t = 2.4 +/- 0.2 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.