2005AJ....129..656C

We present deep JHK photometry of the old and metal-rich open cluster NGC 6791. The photometry reaches below the main-sequence turnoff to K~16.5 mag. We combine our photometry with that from Stetson et al. to provide color-magnitude diagrams showing K versus J-K, K versus V-K, and V versus V-K. We study the slope of the red giant branch in the infrared but find that it is not a useful metallicity indicator for the cluster, nor any metal-rich cluster that lacks a well-populated red giant branch, because it is not linear, as has often been assumed, in K versus J-K. The mean color of the red horizontal-branch/red clump stars provide an estimate of the cluster reddening, E(B-V)=0.14±0.04 mag for [Fe/H]=+0.4±0.1. The mean magnitudes of these stars also provide a good distance estimate, (m-M)₀=13.07±0.04. Finally, we find that the isochrones of Yi et al. provide optimal fits in V versus B-V and V-K and K versus J-K and V-K for such values if [Fe/H] lies between +0.3 and +0.5 (with a slight preference for +0.5) and ages between 9 Gyr ([Fe/H]=+0.3) and 7.5 Gyr ([Fe/H]=+0.5).