The Near-Infrared Photometric Properties of Bright Giants in the Central Regions of the Galactic Bulge

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Abstract
Images recorded through broadband (JHK) and narrowband (CO and 2.2 μm continuum) filters are used to investigate the photometric properties of bright (K ≤ 13.5) stars in a 6' × 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 AK ~ 2.8 mag. Extinction measurements for individual stars are estimated using the MK versus infrared color relations defined by M giants in BW, and the majority of stars have AK between 2.0 and 3.5 mag. The extinction is locally high in the Sgr A complex, where AK ~ 3.1 mag. Reddening-corrected CO indexes, CO0, are derived for over 1300 stars with J, H, and K brightnesses and for over 5300 stars with H and K brightnesses. The distribution of CO0 values for stars with K0 between 11.25 and 7.25 can be reproduced using the MK-CO0 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 μm 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.
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