THE GIANT BRANCHES OF OPEN AND GLOBULAR-CLUSTERS IN THE INFRARED AS METALLICITY INDICATORS - A COMPARISON WITH THEORY

We apply the giant branch slope-[Fe/H] relation derived by Kuchinski e r al. (1995, AJ, 109, 1131) to a sample of open clusters. We find that the slops of the giant branch in K vs (J- K) color-magnitude diagrams correlates with [Fe/H] for open clusters as it does for metal-rich gl obular clusters but that the open cluster data are systematically shif ted to less negative values of giant branch slope, at constant [Fe/H]. We use isochrone models to examine the theoretical basis for this rel ationship and find that for a given value of [Fe/H]. the slope of the relationship remains constant with decreasing population age but the r elation shifts to less negative values of giant branch slope with decr easing age. Both of these theoretical predictions. agree with the tren ds found in the data. Finally, we derive new coefficients for the gian t branch slope [Fe/H] relation for specific members of 3 populations, metal-rich globular clusters, bulge stars and open clusters. (C) 1997 American Astronomical Society.