Resolving the 47 Tucanae Distance Problem

We present new B, V and I-band photometry for a sample of 43 local subdwarfswith HIPPARCOS parallax errors < 13%, in the metallicity range -1.0 < [Fe/H] <-0.3, which we use to perform main sequence (MS) fitting to the Galacticglobular cluster 47 Tuc. This sample is many times larger than those used inprevious MS-fitting studies and also enables us to fit in two colour planes,V/(B-V) and V/(V-I). With this enlarged subdwarf sample we investigate whetherthe current discrepancy in empirical distance estimates for 47 Tuc, arisingfrom recent MS-fitting and white dwarf fitting results, is due to inaccuraciesin the MS-fitting method. Comparison of published photometries for 47 Tuc hasrevealed systematic offsets which mean that the $(B-V)$ main-line used inprevious studies may be too blue by ~ 0.02 mag. We have derived main-lines inV/(B-V) and V/(V-I) from the data of Kaluzny et al. (1998), which we haverecalibrated from the `secondary' standards in 47 Tuc of Stetson (2000). Usingan assumed cluster reddening of E(B-V)=0.04, our best-fit apparent distancemodulus is (m-M)V=13.37 (+0.10)(-0.11) in both colour planes, which implies acluster age of 11.0 +/-1.4 Gyr and leads to a dereddened distance modulus of(m-M)0=13.25 (+0.06)(-0.07). Comparison with previous work shows that ourapparent distance modulus is ~0.2 mag smaller than those derived in previousMS-fitting studies. The difference is accounted for by our preferred clusterreddening and the recalibration of the cluster photometry, which has made themain-line redder by an average of 0.02 mag in (B-V). Independent support forour MS-fitting distance comes from consideration of the Red Clump in thecluster, from which we derive a dereddened distance modulus of (m-M)0=13.31+/-0.05, which is in agreement with the MS-fitting result. (Abridged)Comment: 23 pages, including 2 tables and 4 figures. ApJ accepte