SIMBAD references

We present a detailed study of NGC 6791, NGC 6811, NGC 6819, and NGC 6866, the four open clusters that are located in the Kepler prime field. We use new CCD UBV(RI)_KC photometry, which was combined with Gaia EDR3 photometric/astrometric data, to derive the astrophysical parameters with two-independent methods - one of them the fitCMD algorithm. Furthermore, we provide among others estimates of the mass and mass function, the cluster structure, derive the cluster orbits, and discuss the cluster dynamics. All objects belong to the older open cluster population (∼1-7 Gyr), are in an advanced dynamical stage with signs of mass segregation, and are located close to the solar circle, but show a large range in respect of radii, member stars or observed cluster mass ($\sim 100\!-\!2000\, \mathrm{M}_\odot$). For the three younger objects, we were also able to provide photometric metallicity estimates, which confirms their status as clusters with a roughly solar metallicity. The most outstanding object is clearly NGC 6791, a very old cluster with a high metallicity at a distance of about 4.5 kpc from the Sun. We estimate a probable radial migration by about 7 kpc, resulting in a birth position close to the Galactic centre.