The near-infrared photometric properties of bright giants in the central regions of the galactic bulge

Images recorded through broadband (JHK) and narrowband (CO and 2.2 mu m continuum) filters are used to investigate the photometric properties of bright (K less than or equal to 13.5) stars in a 6' x 6' field centered on the Sgr A complex. The giant branch ridge lines in the (K, J-K) and (K, H-K) color-magnitude diagrams are well matched by the Baade's window (BW) M giant sequence if the mean extinction is A(K) similar to 2.8 mag. Extinction measurements for individual stars are estimated using the M(K) versus infrared color relations defined by M giants in BW, and the majority of stars have A(K) between 2.0 and 3.5 mag. The extinction is locally high in the Sgr A complex, where A(K) similar to 3.1 mag. Reddening-corrected CO indexes, CO(0), are derived for over 1300 stars with J, H, and K brightnesses and for over 5300 stars with PI and K brightnesses. The distribution of CO(0) values for stars with K(0) between 11.25 and 7.25 can be reproduced using the M(K)-CO(0) relation defined by M giants in BW. The data thus suggest that the most metal-rich giants in the central regions of the bulge and in BW have similar photometric properties and 2.3 mu m CO strengths. Hence, it appears that the central region of the bulge does not contain a population of stars that are significantly more metal-rich than what is seen in BW.