Description
We have observed almost one third of the globular clusters in the Milky Way, targeting distant and/or highly reddened objects, as well as a few reference clusters. A large sample of red giant stars was observed with FORS2 at VLT/ESO at R~2000. The method for deriving stellar parameters is presented with application to six reference clusters. We aim at deriving the stellar parameters effective temperature, gravity, metallicity, and {alpha}-element enhancement as well as the radial velocity to confirm the membership of individual stars in each cluster. We analyse the spectra collected for the reference globular clusters NGC 6528 ([Fe/H]~-0.1), NGC 6553 ([Fe/H]~-0.2), M 71 ([Fe/H]~-0.8), NGC 6558 ([Fe/H]~-1.0), NGC 6426 ([Fe/H]~-2.1), and Terzan 8 ([Fe/H]~-2.2). They cover the full range of globular cluster metallicities, and are located in the bulge, disc, and halo. Full spectrum-fitting techniques were applied by comparing each target spectrum with a stellar library in the optical region at 4560-5860{AA}. We employed the library of observed spectra MILES, and the Coelho synthetic library. We validated the method by recovering the known atmospheric parameters for 49 well-studied stars that cover a wide range in the parameter space. We adopted as final stellar parameters (effective temperatures, gravities, metallicities) the average of results using the observed and synthetic spectral libraries.
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