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J.-W. Lee (Yonsei University & California Institute of Technology), B. W. Carney (University of North Carolina)
We present a chemical abundance study of the old inner halo clusters NGC~6287, NGC~6293, and NGC~6541. Our metallicity estimates for NGC~6287, NGC~6293, and NGC~6541 are [Fe/H] = -2.00 ± 0.05, -2.01 ± 0.02, and -1.78 ± 0.02, respectively, and our metallicity measurements are in good agreement with previous estimates.
The mean \alpha-element abundances of our program clusters are in good agreement with other globular clusters, confirming previous results. However, the individual \alpha-elements appear to follow different trends. The silicon abundances of the inner halo clusters appear to be enhanced and the titanium abundances appear to be depleted compared to the intermediate halo clusters. In particular, [Si/Ti] ratios appear to be related to the metallicities or Galactocentric distances, in the sense that [Si/Ti] ratios decrease with metallicity and Galactocentric distance. We propose that these [Si/Ti] gradients with metallicity or Galactocentric distance may be due to the different masses of the SNe II progenitors. The high [Si/Ti] ratios toward the Galactic center and at lower metallicities may be due to high-mass SNe II contributions.