Probable binary open star clusters in the galaxy

Abstract

The existence of double/binary clusters in the Magellanic Clouds is fairly well established, whereas only one such pair, h + χ Persei, is known in the Galaxy. From the catalogues of open clusters of the Galaxy, we have identified 18 probable pairs of clusters (with known distances), with spatial separations less than 20pc. The tidal disruption timescales for these pairs, due to Galactic differential rotation are calculated, using cluster data where available or by assuming typical values. In some cases, these timescales are larger than the average open cluster lifetime, ≈10⁸yr. About 8% of open clusters appear to be members of binary systems, and hence binary cluster systems may not be very uncommon in the Galaxy.