Red Giant Branch Stars as Probes of Stellar Populations I: 2MASS Calibration and Application to 2MASS GC01

摘要

The near-infrared behavior of the red giant branch (RGB hereafter) as afunction of abundance is examined with an unprecedented large sample of 27Galactic globular clusters with Two Micron All Sky Survey photometry. Wepropose a new simplified analyses, involving the zero point of the RGB slopefit, and derive calibrations for the RGB slope, zero point, and tip. The weakmetallicity sensitivity of the zero point leads to a ``fan''-like diagram forobtaining the abundance distributions in resolved stellar systems, andreddening estimates. Finally, we apply the new calibrations to the recentlydiscovered Galactic globular cluster 2MASS GC01, to derive[Fe/H]_H96=-1.19+/-0.38 mag. The uncertainty is dominated by the severeforeground contamination. We estimate an extinction of A_V=21.07+/-2.20 magtoward the cluster.