A comprehensive study of 94 open clusters based on the data from IPHAS, GAIA DR2, and other sky surveys
Abstract
We determine the color excesses, photometric distances, ages, astrometric parallaxes and proper motions for 94 open clusters in the northern part of the Milky Way. We estimate the color excesses and photometric distances based on the data from IPHAS photometric survey of the northern Galactic plane using individual total-to-selective extinction ratios Rr=Ar/E(r-i) for each cluster computed via the color-difference method based on IPHAS r, i, and Halpha-band, 2MASS J, H, and Ks-band, WISE W1-band, and Pan-STARRS i, z, and y-band data. The inferred Rr values vary significantly from cluster to cluster spanning the Rr=3.1--5.2 interval with a mean and standard deviation equal to <Rr>=3.99 and sigma Rr=0.34, respectively. We identified cluster members using (1) absolute proper motions determined from individual-epoch positions of stars retrieved from IPHAS, 2MASS, URAT1, ALLWISE, UCAC5, and Gaia DR1 catalogs and positions of stars on individual Palomar Sky Survey plates reconstructed based on the data provided in USNO-B1.0 catalog and (2) absolute proper motions provided in Gaia DR2 catalog, and computed the average Gaia DR2 trigonometric parallaxes and proper motions of the clusters. The mean formal error of the inferred astrometric parallaxes of clusters is of about 7microarcseconds, however, a comparison of astrometric and photometric parallaxes of our cluster sample implies that Gaia DR2 parallaxes are, on the average, systematically underestimated by 45 +/-9 microarcseconds. This result agrees with estimates obtained by other authors using other objects. At the same time, we find our photometric distance scale to be correct within the quoted errors (the inferred correction factor is equal to unity to within a standard error of 0.025).