Chemical Abundances of Three Metal-poor Globular Clusters (ngc 6287, Ngc 6293, and Ngc 6541) in the Inner Halo

We present a chemical abundance study of three inner old halo clusters NGC 6287, NGC 6293, and NGC 6541, finding [Fe/H] = −2.01 ± 0.05, −1.99 ± 0.02, and −1.76 ± 0.02 (internal), respectively, and our metallicity measurements are in good agreement with previous estimates. We also present the radial velocity measurements of the clusters. Our radial velocity measurements for NGC 6293 and NGC 6541 are in good agreement with previous measurements, however, our radial velocity measurement for NGC 6287 is almost 80 km s larger than the previous measurement. The mean α-element abundances of our program clusters are in good agreement with other globular clusters, confirming previous results. However, the individual α-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. Our results also appear to oppose to those of metal-rich bulge giants studied by McWilliam and Rich, who found that bulge giants are titanium enhanced and silicon deficient. In particular, [Si/Ti] ratios appear to be related to Galactocentric distances, in the sense that [Si/Ti] ratios decrease with Galactocentric distance. We propose that Department of Physics & Astronomy, University of North Carolina, Chapel Hill, NC 27599-3255; [email protected]; [email protected] Center for Space Astrophysics, Yonsei University, Shinchon-dong 134, Seoul 120-749, Korea PMA Division, California Institute of Technology, Mail Stop 405-47, Pasadena, CA 91125, USA; [email protected] Visiting Astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. Inner Halo Clusters 2 contributions from different masses of the SNe II progenitors that enriched protoglobular cluster clouds’ elemental abundances and the different initial physical environments surrounding the proto-globular clusters clouds are responsible for this gradient in [Si/Ti] ratios versus Galactocentric distances of the “old halo” globular clusters. On the other hand, our program clusters’ enhanced s-process elemental abundances suggest that the formation timescale of our program clusters might be as short as a few times 10 yr after the star formation is initiated in the Galaxy’s central regions, if the s-process site is intermediate mass AGB stars. Subject headings: Galaxy: halo — globular clusters: individual (NGC 6287, NGC 6293, NGC 6541) — stars: abundances