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Dynamics of the Globular Cluster NGC 6656 with WFPC2

Chen, Li; Chen, Ding; Wang, Jia-Ji

We have used the Hubble Space Telescope observations to measure proper motion of the globular cluster NGC 6656 (M22) with respect to the background bulge stars and its internal velocity dispersion profile. Based on the proper motion of the cluster, its space velocity (Pi,Theta,W) = (184+/-3, 209+/-14, 132+/-15) km s^-1 and galactic orbit…