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Title: SPACE VELOCITIES OF SOUTHERN GLOBULAR CLUSTERS. VII. NGC 6397, NGC 6626 (M28), AND NGC 6656 (M22)

We have measured the absolute proper motions of globular clusters NGC 6397, NGC 6626 (M22), and NGC 6656 (M28) as part of our ongoing Southern Proper-Motion Program. The reference system is the ICRS via Hipparcos stars for these three low-Galactic-latitude clusters. Formal errors range between {approx}0.3 and 0.7 mas yr{sup -1}. Notable is the result for NGC 6397, which differs by 2.5 mas yr{sup -1} from two Hubble Space Telescope determinations while agreeing with previous ground-based ones. We determine orbits for all three clusters in an axisymmetric and barred model of the Galaxy and discuss these in the context of globular-cluster formation. M22 is a well-known cluster with an iron abundance spread; such clusters are now believed to have formed in massive parent systems that can retain ejecta of core-collapsed supernovae. We find that the five currently accepted globular clusters with iron/calcium abundance spread show orbits unrelated to each other, thus suggesting at least five independent, massive progenitors that have contributed to the build-up of the Milky-Way halo.
Authors:
; ;  [1] ;  [2] ; ;  [3]
  1. Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States)
  2. Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlarska 2, CZ-61137 Brno (Czech Republic)
  3. Universidad National de San Juan, Observatorio Astronomico ''Felix Aguilar'' and Yale Southern Observatory, Chimbas, 5413 San Juan (Argentina)
Publication Date:
OSTI Identifier:
22122889
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 146; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AXIAL SYMMETRY; CALCIUM; GALAXY CLUSTERS; ION CYCLOTRON-RESONANCE; IRON; MILKY WAY; ORBITS; PROPER MOTION; SPACE; SUPERNOVAE; TELESCOPES