A New Look at the Old Star Cluster NGC 6791
Abstract
We present comprehensive cluster membership and g'r' photometry of the prototypical old, metal-rich Galactic star cluster NGC 6791. The proper-motion catalog contains 58,901 objects down to g'=24, limited to a circular area of radius 30 arcmin. The highest precision of the proper motions is 0.08 mas/yr. Our proper motions confirm cluster membership of all main and also some rare constituents of NGC 6791. The total number of probable cluster members down to g'=22 (MV=+8) is 4800, corresponding to Mtot=5000 Msolar. New findings include an extended horizontal branch in this cluster. The angular radius of NGC 6791 is at least 15 arcmin (the effective radius is Rh=4.4 arcmin while the tidal radius is rt=23 arcmin). The luminosity function of the cluster peaks at Mg'=+4.5 and then steadily declines toward fainter magnitudes. Our data provide evidence that differential reddening may not be ignored in NGC 6791.
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