Comparison of globular clusters in Fornax and Sagittarius with those of the Galaxy, and, the Calypso high-resolution telescope.

摘要

Fornax and Sagittarius are the only nearby dwarf spheroidal galaxies known to have globular clusters and, as such, offer a unique opportunity to compare their globular clusters with similar low metallicity clusters of the Galaxy.; We obtained data on Fornax globular clusters from observations of K. Mighell taken with the CTIO 4m telescope in 1993. Our color-magnitude diagrams for Fornax clusters 1 and 5 reach below the horizonal branch to V = 24 and our measured horizonal branch colors shows clusters 1 and 5 to be the first extragalactic second parameter pair. We find 21 possible variable stars out of 41 horizonal branch stars both within and outside of the instability strip. Our color-magnitude diagrams for Fornax cluster 3 reach below the horizonal branch to V = 23. Cluster 3 is located in a denser field of the galaxy, and we carried out the first field subtraction. Our calculated horizonal branch type indicates clusters 1 and 3 to be a second parameter pair. We found 7 variable stars. Using our Fornax results and the latest published data on the Sagittarius globular clusters, we made comparisons with similar low metalicity Galactic clusters using horizonal branch types and metalicities. The Fornax clusters are somewhat redder than old halo clusters. The three metal poor Sagittarius clusters are bluer than the Fornax clusters and most resemble the LMC and old halo clusters. Neither cluster system seems like the younger halo clusters often suggested to have been accreted from disrupted dwarf spheroidal galaxies. We found no correlation between horizonal branch types and central concentration.; Over the past eight years I have promoted, conceptualized, and constructed with a team of engineers the Calypso telescope which is designed to get high resolution on bright objects such as globular clusters. Tests at the Kitt Peak site indicate best quartile 0.25″ seeing. The telescope has both tip-tilt and 10' FOV cameras. The 17th wave very smooth optics and stringent baffling reduce scattered light. A roll off enclosure eliminates dome seeing.