Revisit of Open Clusters UPK 39, UPK 41, and PHOC 39: A New Binary Open Cluster Found

Abstract

We investigate the three open clusters near the Aquila Rift cloud, named UPK 39 (c1 hereafter), UPK 41 (c2 hereafter) in Sim et al. (2019), and PHOC 39 (c3 hereafter) in Hunt & Reffert (2021). Using photometric passpands, reddening, and extinction from Gaia DR3, we construct the color-absolute-magnitude diagram. Using isochrone fits, their ages are estimated as 6.3 ± 0.9, 8.1 ± 1.4 and 21.8 ± 2.2 Myr. Their proper motions and radial velocities, estimated using data from Gaia and LAMOST, are very similar. From their orbits, relative distances among them at different times, kinematics, ages, and metallicities, we conclude that c1 and c2 are primordial binary open cluster, which are likely to have been formed at the same time, and c3 may capture c1, c2 in the future.