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| Paper: |
The Age of NGC 5927: Formation Timescales of the Halo and Thick Disk |
| Volume: |
92, Formation of the Galactic Halo. . . . Inside and Out |
| Page: |
269 |
| Authors: |
Fullton, L. K.; Carney, B. W.; Olszewski, E. W.; Zinn, R.; Demarque, P.; Da Costa, G. S.; Janes, K. A.; Heasley, J. N. |
| Abstract: |
We present the HST WFPC2 VIC color-magnitude diagram (CMD) of the metal-rich (thick) disk globular cluster NGC 5927. Our CMD indicates that NGC 5927 is somewhat younger than other disk globular clusters with known ages. Observations of the relative numbers of stars on the RGB and RHB indicate a large helium abundance, Y = +0.29+/-0.04. Comparison of the seven known thick disk globular clusters that have estimated ages with ages of globulars that belong to the halo reveals a significant overlap in age between the two cluster systems. As a group, the disk clusters appear somewhat younger than their halo counterparts, indicating that the Galactic halo began to form some 1--2 Gyr before the thick disk, in agreement with studies by Carney et al. (1990) and Marquez & Schuster (1994). |
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