Red giant branch stars as probes of stellar populations. I. 2MASS calibration and application to 2MASS GC01

¹ European Southern Observatory, Ave. Alonso de Cordova 3107, Casilla 19, Santiago 19001, Chile
² Institute of Astronomy, Bulgarian Academy of Sciences, and Isaac Newton Institute of Chile, Bulgarian Branch, 72 Tsarigradsko Chaussèe, 1784 Sofia, Bulgaria e-mail: jura@haemimont.bg

Corresponding author: V. D. Ivanov, vivanov@eso.org

Received: 16 January 2002
Accepted: 24 April 2002

Abstract

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 analysis, 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 to obtain 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] mag. The uncertainty is dominated by the severe foreground contamination. We estimate an extinction of mag toward the cluster.