The Astronomical Journal
Hubble Space Telescope (V, I) photometry has been obtained for the inner halo globular cluster NGC 6652. The photometry reaches ~4 mag below the turnoff and includes a well-populated horizontal branch. This cluster is located close to the Galactic center, at RGC 2.0 kpc, with a reddening of E(V-I) = 0.15 ± 0.02, and has a metallicity of [Fe/H] -0.85. Based upon ΔV, NGC 6652 is 11.7 ± 1.6 Gyr old. Using ΔV, precise differential ages for 47 Tuc (a thick disk globular cluster), M107, and NGC 1851 (both halo clusters) were obtained. NGC 6652 appears to be the same age as 47 Tuc and NGC 1851 (within ±1.2 Gyr), while there is a slight suggestion that M107 is older than NGC 6652 by 2.3 ± 1.5 Gyr. As this is a less than 2 σ result, this issue needs to be investigated further before a definitive statement regarding the relative age of M107 and NGC 6652 may be made.
Chaboyer, Brian; Sarajedini, Ata; and Armandroff, Taft E., "The Age of the Inner Halo Globular Cluster NGC 6652" (2000). Open Dartmouth: Faculty Open Access Articles. 3386.