Astrometric and photometric study of Dias 4, Dias 6, and other five open clusters using ground-based and Gaia DR2 data

W. S. Dias, H. Monteiro, J. R.D. Lépine, R. Prates, C. D. Gneiding, M. Sacchi

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We present a study of seven southern open clusters based on UBVRI CCD photometry (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 catalogue, 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.

Original languageEnglish
Pages (from-to)3887-3901
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date23 Aug 2018
Publication statusPublished - 11 Dec 2018


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