A comprehensive study of 94 open clusters based on the data from IPHAS, GAIA DR2, and other sky surveys

TL;DR

This study analyzes 94 open clusters using data from multiple sky surveys to determine their physical properties, revealing significant variation in extinction ratios and systematic underestimation in Gaia DR2 parallaxes.

Contribution

It provides a comprehensive multi-survey analysis of open clusters, including new estimates of extinction ratios and a correction for Gaia DR2 parallax systematic errors.

Findings

R_r extinction ratios vary from 3.1 to 5.2 with mean 3.99

Gaia DR2 parallaxes are systematically underestimated by about 45 microarcseconds

Photometric distance scale is validated within errors

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 R_r=A_r/E_(r-i) for each cluster computed via the color-difference method based on IPHAS r, i, and H_alpha-band, 2MASS J, H, and K_s-band, WISE W1-band, and Pan-STARRS i, z, and y-band data. The inferred R_r values vary significantly from cluster to cluster spanning the R_r=3.1--5.2 interval with a mean and standard deviation equal to <R_r>=3.99 and sigma R_r=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).