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Paper: Slowly Orbiting Old Open Clusters in the Galactic Outerdisk
Volume: 458, Galactic Archaeology: Near-Field Cosmology and the Formation of the Milky Way
Page: 223
Authors: Hasegawa, T.; Sakamoto, T.
Abstract: Slowly orbiting old open clusters are reported in the outerdisk of the Galaxy by means of radial velocity measurements. Clusters in question are estimated to be 2 ∼ 5 Gyr old around the putative Canis Major dwarf galaxy (the Galactocentric distances are 10 ∼ 15 kpc). Not a small fraction of old clusters in this field are orbiting 30 ∼ 50 km s-1 slower than the rotation of the Galactic disk. Though the sample is incomplete, there seems some mechanism that make these clusters rotate slowly, such as the warp of the Galactic disk and/or merging process of the Canis Major dwarf galaxy. The former possibility is less favored when compared with dynamics of young clusters.
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