B. Dias Abstract Talk

Metallicities and Alpha-to-Iron Ratios in Globular Clusters Stars in a Homogeneous Scale - Search for Multiple Populations

B. Dias (IAG-USP/ESO), I. Saviane, B. Barbuy, E. Held, G. Da Costa, S. Ortolani, and S. Vasquez

We are carrying out a survey of 51 poorly studied Milky Way globular clusters, by means of spectroscopy of ~20 red giants per cluster. Optical spectra (4600-5800 A) were obtained with FORS2 at VLT/ESO, at a resolution Delta lambda ~ 2.5 A. We use ETOILE code (Katz et al. 2011) to derive radial velocities, Teff, log g, [Fe/H] and [Mg/Fe] for each star, by finding the best fitting spectrum among a grid of observed stars of ELODIE and MILES libraries, as well as a synthetic library (Coelho et al. 2005). Another code (HALO, Cayrel et al. 1991) is used to fit spectra in a different way using synthetic spectra. The main contributions of this work are: to provide a homogeneous scale of [Fe/H], [Mg/Fe], and radial velocities for the 51 clusters -- in particular for the 29 distant and/or highly reddened ones -- to provide a catalogue of confirmed member stars for each cluster, in addition to find interesting cases for follow-up with high resolution data (like the massive clusters M 22, and NGC 5824, for which we found a spread in [Fe/H]).