The near-infrared behavior of the red giant branch ( RGB hereafter ) as a function of abundance is examined with an unprecedented large sample of 27 Galactic globular clusters with Two Micron All Sky Survey photometry .
We propose a new simplified analyses , involving the zero point of the RGB slope fit , and derive calibrations for the RGB slope , zero point , and tip .
The weak metallicity sensitivity of the zero point leads to a “ fan ” -like diagram for obtaining the abundance distributions in resolved stellar systems , and reddening estimates .
Finally , we apply the new calibrations to the recently discovered Galactic globular cluster 2MASS GC01 , to derive [ Fe/H ] _ { H 96 } = -1.19 \pm 0.38 mag .
The uncertainty is dominated by the severe foreground contamination .
We estimate an extinction of A _ { V } = 21.07 \pm 2.20 mag toward the cluster .