Detection of tidal tails around the open cluster M 67 using principal component analysis

Abstract

Abstract In this paper we present an investigation of tidal tails around the old open cluster M 67 using Gaia-DR2. We identify likely extra-tidal stars around M 67 using principal component analysis (PCA) and a Gaussian mixture model (GMM). We find 1618 stars closely related to M 67, 85 of which are likely extra-tidal stars. We find clear evidence for the existence of two well-defined tidal tails emerging from M 67. The tidal tails extend out to projected distances of at least ${2{^{\circ}_{.}}5}$ (∼39 pc), which is more than twice as large as the tidal radius of the cluster. Based on LAMOST-DR5 data, we confirm that 13 extra-tidal stars have radial velocities and metallicities similar to those of the cluster. Furthermore, we also confirm that the extra-tidal stars cover a wide mass range of 0.2–1.1 M⊙, and nearly half the extra-tidal stars are less than 0.57 M⊙. The total mass of the extra-tidal stars is determined to be about 55 M⊙. We estimate a mass-loss rate of ∼2.8 M⊙ Myr−1 for M 67. Possible origins of these extra-tidal stars are discussed.