Near-infrared properties of metal-poor globular clusters in the Galactic bulge direction

Aims. J, H, and K′ images obtained from the near-infrared imager CFHTIR on the Canada-France-Hawaii Telescope are used to derive the morphological parameters of the red giant branch (RGB) in the near-infrared color-magnitude diagrams for 12 metal-poor globular clusters in the Galactic bulge direction. Using the compiled data set of the RGB parameters for the observed 12 clusters, in addition to the previously studied 5 clusters, we discuss the properties of the RGB morphology for the clusters and compare them with the calibration relations for the metal-rich bulge clusters and the metal-poor halo clusters. Methods. The photometric RGB shape indices, such as colors at fixed magnitudes of M_K = M_H = (-5.5, -5, -4, and -3), magnitudes at fixed colors of (J-K)_o = (J-H)_o = 0.7, and the RGB slope, were measured from the fiducial normal points defined in the near-infrared color-magnitude diagrams for each cluster. The magnitudes of RGB bump and tip were also estimated from the differential and cumulative luminosity functions of the selected RGB stars. The derived RGB parameters were used to examine the overall behaviors of the RGB morphology as a function of cluster metallicity. Results. The correlations between the near-infrared photometric RGB shape indices and the cluster metallicity for the program clusters compare favorably with the previous observational calibration relations for metal-rich clusters in the Galactic bulge and the metal-poor halo clusters. The observed near-infrared magnitudes of the RGB bump and tip for the investigated clusters also accord with the previous calibration relations for the Galactic bulge clusters.