Astrometric and photometric study of Dias 4, Dias 6 and other five open
  clusters using ground based and Gaia DR2 data
  We present a study of 7 southern open clusters based on UBVRI CCD photomety
(Johnsons-Cousins system) and Gaia DR2 data. Dias 4, Dias 6 and four other
clusters had UBVRI photometric observations determined for the first time. From
the observational UBVRI data we obtained photometric membership probability
estimates and, using the proper motions from the UCAC5 catalog, we also
determined the kinematic membership. From Gaia DR2 astrometric data we
determine the stellar membership using proper motions and parallaxes, taking
into account the full covariance matrix. For both independent sets of data and
membership we apply our non subjective multidimensional global optimization
tool to fit theoretical isochrones to determine the distance, age, reddening,
metallicity and binary fraction of the clusters. The results of the mean proper
motions, distances and ages are in agreement, but the ones obtained from Gaia
DR2 data are more precise in both membership selection and estimated
parameters. In the case of NGC 6087, the Cepheid S Nor, member of the open
cluster, was used to obtain an independent distance estimate, confirming the
one determined by our fitting method. We also report a serendipitous discovery
of two new clusters in the extended field near what was originally Dias 4.
