期刊
ASTRONOMICAL JOURNAL
卷 146, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-6256/146/2/33
关键词
astrometry; Galaxy: kinematics and dynamics; Galaxy: structure; globular clusters: individual (NGC 6397, NGC 6626/M28, NGC 6656/M22)
资金
- NSF [AST04-0908996]
- NASA
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0908996] Funding Source: National Science Foundation
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 similar to 0.3 and 0.7 mas yr(-1). Notable is the result for NGC 6397, which differs by 2.5 mas yr-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.
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