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We review ve independent techniques that are used to set the distance scale to globular clusters, including subdwarf main-sequence tting utilizing the recent Hipparcos parallax catalog. These data together all indicate that globular clusters are farther away than previously believed, implying a reduction in age estimates. We now adopt a best-t value (RR Lyrae stars) \ 0. 39 ⁰. 08 (statistical) M v at Fe/H \ [1. 9 with an additional uniform systematic uncertainty of This new distance scale ~0. 18 `0. 13. estimate is combined with a detailed numerical Monte Carlo study (previously reported by Chaboyer et al. ) designed to assess the uncertainty associated with the theoretical ageturno luminosity relationship in order to estimate both the absolute age and uncertainty in age of the oldest globular clusters.
Chaboyer et al. (Tue,) studied this question.