The globular cluster NGC 6723 and the age of the Galactic Bulge

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Session 74 -- Globular Clusters
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[74.06] The globular cluster NGC 6723 and the age of the Galactic Bulge

L. K. Fullton, B. W. Carney (UNC-CH)

We present CCD-based BV photometry of the globular cluster NGC 6723 and construct the color-magnitude diagram (CMD) from the tip of the giant branch to several magnitudes below the main-sequence turnoff. NGC 6723 is located at a distance of $\sim$2.7 kpc directly below the Galactic Center and has [Fe/H]= $-$1.1 (Zinn \& West 1984 ApJS, 55, 45). Lee (1992 AJ, 104, 1780) has claimed that the bulge is the Galaxy's oldest component based on the mean metalliticity of the RR Lyraes in Baade's Window (BW) and his models of the horizontal branch. NGC 6723 is an important test cluster for this hypothesis. Its metallicity is comparable to the mean metallicity derived by Walker and Terndrup ([Fe/H] = $-$1.0; 1991 ApJ, 386, 663) for the BW RR Lyraes, and it lies reasonably close to the Galactic center in a region of low reddening. The available kinematics of NGC 6723 are consistent with membership in a bulge-like component. We determine the age of NGC 6723 from the CMD, discuss its implications for Lee's hypothesis, and present suggestions for future studies.

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