Deep Near‐Infrared Array Photometry of Globular Clusters. VI. NGC 288

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Abstract
Deep J and K' images are used to construct a K, J-K color-magnitude diagram (CMD) of the moderately metal-poor halo globular cluster NGC 288. The CMD extends from the upper giant branch to below the main-sequence turnoff (MSTO), and comparisons with [Fe/H] = -1.26 oxygen-enhanced near-infrared isochrones derived from the optical sequences tabulated by Bergbusch & Vandenberg are suggestive of an age in excess of 16 Gyr. Comparisons with near-infrared fiducial sequences for the clusters M4 (Davidge & Simons 1994) and M28 (Davidge, Côté, & Harris 1996) indicate that (1) the ratio of selective extinction in V to E(B-V), RV, is roughly 4 toward M4, which is consistent with previous optical studies; and (2) M4 and M28 appear to be at least as old as NGC 288. Published optical data are used to check some of these results. The color and brightness of the NGC 288 MSTO at optical wavelengths are consistent with an age near 16 Gyr, while a comparison of the optical CMDs of NGC 288 and M4 suggest that the latter is at least as old as the former. This is consistent with the conclusion drawn from the near-infrared CMDs, but it is contrary to what might be expected based on the color distribution of horizontal branch stars in these clusters.