A binary star sequence in the outskirts of the disrupting Galactic open
  cluster UBC 274
  We report the identification of a numerous binary star population in the
recently discovered ~3 Gyr old open cluster UBC 274. It becomes visible once
the cluster color-magnitude diagram is corrected by differential reddening and
spans mass ratios (q) values from 0.5 up to 1.0. Its stellar density radial
profile and cumulative distribution as a function of the distance from the
cluster's center reveal that it extends out to the observed boundaries of the
cluster's tidal tails (~ 6 times the cluster's radius) following a spatial
distribution indistinguishable from that of cluster Main Sequence (MS) stars.
Furthermore, binary stars with q values smaller or larger than 0.75 do not show
any spatial distribution difference either. From Gaia DR2 astrometric and
kinematics data we computed Galactic coordinates and space velocities with
respect to the cluster's center and mean cluster space velocity, respectively.
We found that, cluster members located all along the tidal tails, irrespective
of being a single or binary star, move relatively fast. The projection of their
motions on the Galactic plane resembles that of a rotating solid body, while
those along the radial direction from the Galactic center and perpendicular to
the Galactic plane suggest that the cluster is being disrupted. The similarity
of the spatial distributions and kinematic patterns of cluster MS and binary
stars reveals that UBC 274 is facing an intense process of disruption that has
apparently swept out any signature of internal dynamic evolution like mass
segregation driven by two-body relaxation.
