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