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Session 35 - Old Stellar Populations Beyond the Milky Way - I.
Oral session, Wednesday, June 11
North Main Hall A,
The most recent HST results on 8 globular clusters in M31 will be discussed. The clusters range in metallicity from [Fe/H] \sim --0.4 to \sim --1.8, and lie at projected distances of \sim 4.5 to \sim 34 kpc from the nucleus. Color-magnitude diagrams have been derived from WFPC2 and FOC+COSTAR data. The morphologies of the CMDs indicate metallicities that are generally in good agreement with those estimated from the ground using either spectral indices or suitably calibrated (V-K) colors. These clusters show very similar characteristics to their Galactic counterparts. The relation between the horizontal branch absolute magnitude and the metallicity has a slope of \sim 0.13, fully consistent with the requirements of standard evolutionary models and other independent estimates (e.g. Baade-Wesselink and statistical parallaxes methods on field RR Lyraes), but more difficult to reconcile with higher values (\sim 0.30) also obtained in the past. The uncertainties, however, are still quite large and the forthcoming WFPC2 observations of 10 more clusters will be essential to define this relationship with better accuracy.
