Distances and ages of NGC 6397, NGC 6752 and 47 Tuc

• DOI: 10.1051/0004-6361:20031003
• Publication Date: 2003-08-29T13:57:13Z
• Authors: R. G. Gratton; A. Bragaglia; E. Carretta; G. Clementini; S. Desidera; F. Grundahl; S. Lucatello
• Keywords: Absolute magnitude

New improved distances and absolute ages for the Galactic globular clusters NGC 6397, 6752, 47 Tuc are obtained using Main Sequence Fitting Method. We derived accurate estimates of reddening metal abundance these three a strictly differential procedure, where Johnson Strömgren colours UVES high resolution spectra turn-off stars early subgiants belonging to were compared similar data field subdwarfs with parallaxes measured by Hipparcos. The use free temperature indicator (the profile Hα) allowed us reduce error bars in determinations about 0.005 mag, abundances 0.04 dex, scales defined local subdwarfs. Error then reduced 0.07 mag each cluster, yielding typical random errors 1 Gyr. find that 6397 6752 have Gyr respectively, when standard isochrones without microscopic diffusion used, while is probably 2.6 younger, agreement results other techniques sensitive relative ages. If we models include effects sedimentation due our observations take into account various sources possible systematic statistical approach, conclude age oldest Galaxy Gyr, first bar accounts effects, second one errors. This estimate fully compatible very recent from WMAP, indicates formed within 1.7 after Big Bang, corresponding redshift , ΛCDM model. epoch formation (inner halo) lasted ending at time . On hand, new once combined values H0 given WMAP HST Key Project, provides robust upper limit 95% level confidence independently type Ia SNe, strongly supports need dark energy. cluster lead horizontal branch luminosity, may be used derive zero point relation between magnitude metallicity: obtain 0.03 shorter than Carretta et al. ([CITE]) it agrees with, but more precise most previous individual RR Lyrae magnitude. When apparent average luminosity LMC Clementini ([CITE]), this distance modulus LMC: