Binary open clusters in the Gaia data

¹ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, PR China
e-mail: aliyi@xao.ac.cn; songfangf@xao.ac.cn
² University of Chinese Academy of Sciences, Beijing 100049, PR China

Received: 11 March 2022
Accepted: 16 August 2022

Abstract

Context. Observations indicate that the fraction of potential binary star clusters in the Milky Way is either the same or lower than that of the Magellanic Clouds. The unprecedented precision in the parallax measurements by Gaia has allowed for the discovery of a growing number of new binary open clusters (OCs).

Aims. We aim to survey the candidates of truly binary open clusters that are formed simultaneously, using information from the Gaia database.

Methods. Based on the most recent catalog of open clusters, we investigated the interactions of adjacent binary open clusters in our Galaxy within separations of 50 pc. We compared their coordinates, proper motions, parallaxes, and color-magnitude diagrams (CMDs) via binary plots for all candidate pairs. The candidates of truly binary open clusters are selected on the basis of their common proper motions and consistent behaviors in the CMDs of different clusters that are limited to a separation of 50 pc.

Results. About ten pairs of the selected binary open clusters appear to be the same clusters, based on evidence that almost half of the cluster members are shared. Fourteen pairs are possibly true binaries, implying that they may come from the same clouds, among which five pairs are newly discovered. In addition, two clusters, UBC 46 and UBC 192, were found to be part of the stellar complex LISCA I. Our results confirm that OCs born in groups are usually composed of young open clusters.