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 NGC6287, NGC 6293, and NGC 6541, finding [Fe/H] = -2.01 +/- 0.05, -1.99 +/- 0.02,and -1.76 +/- 0.02, respectively, and our metallicity measurements are in goodagreement with previous estimates. The mean alpha-element abundances of ourprogram clusters are in good agreement with other globular clusters, confirmingprevious results. However, the individual alpha-elements appear to followdifferent trends. The silicon abundances of the inner halo clusters appear tobe enhanced and the titanium abundances appear to be depleted compared to theintermediate halo clusters. Our results also appear to oppose to those ofmetal-rich bulge giants studied by McWilliam and Rich, who found that bulgegiants 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 thatcontributions from different masses of the SNe II progenitors that enrichedproto-globular cluster clouds' elemental abundances and the different initialphysical environments surrounding the proto-globular clusters clouds areresponsible for this gradient in [Si/Ti] ratios versus Galactocentric distancesof the "old halo" globular clusters. On the other hand, our program clusters'enhanced s-process elemental abundances suggest that the formation timescale ofour program clusters might be as short as a few times 10^8 yr after the starformation is initiated in the Galaxy's central regions, if the s-process siteis intermediate mass AGB stars.Comment: Accepted for publication in AJ (Sept. 2002