AbstractThe superior resolution and large format of the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) make it a powerful new tool in the study of extra-galactic globular cluster (GC) systems. We summarize some early results on GC populations from the ACS GTO program, concentrating on the extreme cases of the isolated dwarf NGC 2915 and the core of the massive lensing cluster Abell 1689.
AbstractHigh resolution imaging observations of the core of the globular cluster 47 Tucanae with the Faint Object Camera (FOC) on the Hubble Space Telescope (HST) reveal a very high surface density of blue stragglers. This discovery supports the hypothesis that they are among the most massive objects in globular clusters, concentrated in the core by mass segregation. Taken together with the presence in 47 Tue of an X-ray source, eleven millisecond and binary pulsars, and two high-velocity stars ejected out of the core, these observations favour the scenario that blue stragglers are either mergers formed through coalescent collisions, or binaries formed through close encounters.
Extreme Globular Cluster Systems