Theoretical uncertainties in the subgiant mass-age relation and the absolute age of ω centauri

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 σ uncertainty of ± 2.9% in the derived ages. The theoretical error budget is dominated by the uncertainties in the calculated opacities. Observations by Kałuzny et al. of detached double-lined eclipsing binary OGLEGC 17 in the globular cluster ω Centauri have found that the primary is on the subgiant branch with a mass of M = 0.809 ± 0.012 M_⊙ and [Fe/H] = -2.29 ± 0.15. 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.