The theoretical uncertainties in the calibration of the relationship between
the subgiant mass and age in metal-poor stars are investigated using a Monte
Carlo approach. Assuming that the mass and iron abundance of a subgiant star
are known exactly, uncertainties in the input physics used to construct stellar
evolution models and isochrones lead to a Gaussian 1-sigma uncertainty of
+/-2.9% in the derived ages. The theoretical error budget is dominated by the
uncertainties in the calculated opacities.
Observations of detached double lined eclipsing binary OGLEGC-17 in the
globular cluster Omega Cen have found that the primary is on the subgiant
branch with a mass of M = 0.809+/-0.012 M_sun and [Fe/H]= -2.29+/-0.15 (Kaluzny
et al. 2001). Combining the theoretical uncertainties with the observational
errors leads to an age for OGLEGC-17 of 11.10+/-0.67 Gyr. The one-sided, 95%
lower limit to the age of OGLEGC-17 is 10.06 Gyr, while the one-sided, 95%
upper limit is 12.27 Gyr.Comment: 4 pages, 3 figures, to appear in ApJ
