The Age, Extinction, and Distance of the Old, Metal-rich Open Cluster NGC 6791

Abstract

An extensive grid of metal-rich isochrones utilizing the latest available input physics has been calculated for comparison with the old, metal-rich open cluster NGC 6791. The isochrones have been simultaneously fitted to BV and VI color-magnitude diagrams, with the same composition, reddening, and distance modulus required for both colors. Our best-fitting isochrone assumes [Fe/H]=+0.4, scaled solar abundance ratios, and DeltaY/DeltaZ=2 (Y=0.31), yielding an excellent fit to the data at all points along the major sequences. The resulting age is 8 Gyr, with E(B-V)=0.10 and (m-M)_V=13.42. The derived cluster parameters are fairly robust to variations in the isochrone [Fe/H] and helium abundances. All the acceptable fits indicate that 0.08