Astron. J., 120, 1853-1875 (2000/October-0)
A near-infrared photometric survey of metal-poor inner spheroid globular clusters and nearby bulge fields.
Abstract (from CDS):
Images recorded through J, H, K, 2.2 µm continuum, and CO filters have been obtained of a sample of metal-poor ([Fe/H]≤-1.3) globular clusters in the inner spheroid of the Galaxy. The shape and color of the upper giant branch on the (K, J-K) color-magnitude diagram (CMD), combined with the K brightness of the giant branch tip, are used to estimate the metallicity, reddening, and distance of each cluster. CO indices are used to identify bulge stars, which will bias metallicity and distance estimates if not culled from the data. The distances and reddenings derived from these data are consistent with published values, although there are exceptions. The reddening-corrected distance modulus of the Galactic center, based on the Carney et al. horizontal-branch (HB) brightness calibration, is estimated to be 14.9±0.1. The mean upper giant branch CO index shows cluster-to-cluster scatter that (1) is larger than expected from the uncertainties in the photometric calibration and (2) is consistent with a dispersion in CNO abundances comparable to that measured among halo stars. The luminosity functions (LFs) of upper giant branch stars in the program clusters tend to be steeper than those in the halo clusters NGC 288, NGC 362, and NGC 7089. The majority of inner spheroid clusters fall along the integrated J-K versus metallicity relation defined by halo clusters; however, many of the inner spheroid clusters do not follow the relation between integrated CO index and metallicity measured for halo clusters, in that they have CO indices that are too small. Bulge fields were also observed near most clusters. The slope of the giant branch LF does not vary significantly between most fields, although the LFs in Baade's window and near NGC 6273 are significantly shallower than average. Metallicities estimated from the slope of the upper giant branch on the (K, J-K) CMDs of fields within 6° of the Galactic center are consistent with previous studies. Finally, the data suggest that the HB content may not be uniform throughout the bulge, in the sense that a larger than average number of red HB stars may occur in fields closest to the Galactic center.
Galaxy: Center - Galaxy: Structure - Galaxy: Globular Clusters: General - infrared: radiation - Stars: Horizontal-Branch - Stars: Late-Type
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