... 47 Tuc

Based on data collected at the European Southern Observatory, Chile, telescopes (program 165.L-0263).

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... distance

For instance, Chaboyer & Krauss (2002) have recently derived the age of the double-lined detached binary OGLE17GC in $\omega$ Cen from the location of the two components in the colour-magnitude diagram and their masses, independently of the cluster distance. The derived age  $t=11.1\pm 0.7$ Gyr is compatible with those obtained for the clusters analyzed in the present paper. We also note that $\omega$ Cen is a very peculiar object, perhaps the nucleus of a now dissolved nucleated dwarf elliptical, and its age may well be different from the age of the bulk of Galactic globular clusters.

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... respectively

A downward correction to MSF distances by about 0.1 mag was already suggested by Carretta et al. (2000) based on a comparison of distances derived by this technique with other values. This difference was there attributed to small inconsistencies in the reddening and metallicity scales for globular cluster and local subdwarfs. This correction is confirmed both in sign and size by the present analysis that uses a new homogeneous evaluation of reddenings and metallicities for globular clusters. Indeed, our distance scale is very similar to that final one adopted by Carretta et al. (2000).

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... HB stars

Actually, theoretical models predict the luminosity of the Zero Age Horizontal Branch (ZAHB) and its dependence on metallicity. The correction of the theoretical $M_V({\rm ZAHB}){-}[\rm Fe/H]$ relation to the observed $M_V({\rm HB}){-}[\rm Fe/H]$relation is made either applying a fixed offset that takes into account evolution (generally of the order of 0.08-0.10 mag) or using an empirical correction as the one derived by Sandage (1993) $\Delta V({\rm ZAHB - HB}) = 0.05 {{\rm [Fe/H]}} + 0.16$. This relation corresponds to an evolutionary correction of about 0.085 mag at  $[{\rm Fe/H}]=-1.5$.

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... results

The main difference between the two approaches is that contribution by the various sources of errors are assumed to be uncorrelated in the analysis of Carretta et al., while possible correlations are included in the approach of Chaboyer et al.

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