Open Clusters as Tracers on Radial Migration of the Galactic Disk

Abstract: Radial migration is an important process in the Galactic disk. A few open clusters show some evidence on this mechanism but there is no systematic study. In this work, we investigate the role of radial migration on the Galactic disk based on a large sample of 146 open clusters with homogeneous metallicity and age from Netopil et al. and kinematics calculated from Gaia DR2. The birth site Rb, guiding radius Rg and other orbital parameters are calculated, and the migration distance |Rg-Rb| is obtained, which is a combination of metallicity, kinematics and age information. It is found that 44% open clusters have |Rg-Rb|< 1 kpc, for which radial migration (churning) is not significant. Among the remaining 56% open clusters with |Rg-Rb|> 1 kpc, young ones with t<1.0 Gyr tend to migrate inward, while older clusters usually migrate outward. Different mechanisms of radial migration between young and old clusters are suggested based on their different migration rates, Galactic locations and orbital parameters. For the old group, we propose a plausible way to estimate migration rate and obtain a reasonable value of 1.5(+-0.5) kpc/Gyr based on ten intermediate-age clusters at the outer disk, where the existence of several special clusters implies its complicate formation history.