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We have measured the absolute proper motions of globular clusters NGC 6397,NGC 6626 (M 22) and NGC 6656 (M 28) as part of our ongoing SouthernProper-Motion Program. The reference system is the ICRS via Hipparcos stars forthese three low galactic latitude clusters. Formal errors range between ~0.3and 0.7 mas/yr. Notable is the result for NGC 6397 which differs by 2.5 mas/yrfrom two HST determinations, while agreeing with previous ground-based ones. Wedetermine orbits for all three clusters in an axisymmetric and barred model ofthe Galaxy and discuss these in the context of globular-cluster formation. M 22is a well-known cluster with an iron abundance spread; such clusters are nowbelieved to have formed in massive parent systems that can retain ejecta ofcore-collapsed SNe. We find that the five currently-accepted globular clusterswith iron/calcium abundance spread show orbits unrelated to each other, thussuggesting at least five independent, massive progenitors that have contributedto the build-up of the Milky-Way halo.

Space Velocities of Southern Globular Clusters VII. NGC 6397, NGC 6626 (M 28) and NGC 6656 (M 22)