We present radial velocities and chemical abundances of O , Na , Mg , Al , Si , Ca , Cr , Fe , Co , Ni , and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near ( l , b ) = ( + 5.25 , –3.02 ) and ( 0 , –12 ) .
The ( + 5.25 , –3.02 ) field also includes observations of the bulge globular cluster NGC 6553 .
The results are based on high resolution ( R \sim 20,000 ) , high signal–to–noise ( S/N \ga 70 ) FLAMES–GIRAFFE spectra obtained through the ESO archive .
However , we only selected a subset of the original observations that included spectra with both high S/N and that did not show strong TiO absorption bands .
The present work extends previous analyses of this data set beyond Fe and the \alpha –elements Mg , Si , Ca , and Ti .
While we find reasonable agreement with past work , the data presented here indicate that the bulge may exhibit a different chemical composition than the local thick disk , especially at [ Fe/H ] \ga –0.5 .
In particular , the bulge [ \alpha /Fe ] ratios may remain enhanced to a slightly higher [ Fe/H ] than the thick disk and the Fe–peak elements Co , Ni , and Cu appear enhanced compared to the disk .
There is also some evidence that the [ Na/Fe ] ( but not [ Al/Fe ] ) trends between the bulge and local disk may be different at low and high metallicity .
We also find that the velocity dispersion decreases as a function of increasing [ Fe/H ] for both fields , and do not detect any significant cold , high velocity population .
A comparison with chemical enrichment models indicates that a significant fraction of hypernovae are required to explain the bulge abundance trends , and that initial mass functions that are steep , top–heavy ( and do not include strong outflow ) , or truncated to avoid including contributions from stars > 40 M _ { \odot } are ruled out , in particular because of disagreement with the Fe–peak abundance data .
For most elements , the NGC 6553 stars exhibit nearly identical abundance trends to comparable metallicity bulge field stars .
However , the star–to–star scatter and mean [ Na/Fe ] ratios appear higher in the cluster , perhaps indicating additional self–enrichment .