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NGC 6791 is an old, metal-rich star cluster normally considered to be a diskopen cluster. Its red giant branch is broad in color yet, to date, there is noevidence for a metallicity spread among its stars. The turnoff region of themain sequence is also wider than expected from broad-band photometric errors.Analysis of the color-magnitude diagram reveals a color gradient between thecore of the cluster and its periphery; we evaluate the potential explanationsfor this trend. While binarity and photometric errors appear unlikely,reddening variations across the face of the cluster cannot be excluded. Weargue that a viable alternative explanation for this color trend is an agespread resulting from a protracted formation time for the cluster; the stars ofthe inner region of NGC 6791 appear to be older by ~1 Gyr on average than thoseof the outer region.

Evidence for Extended Star Formation in the Old, Metal-Rich Open Cluster, NGC 6791?