Metallicities and alpha-to-iron ratios in globular clusters stars in a homogeneous scale - Search for multiple populations

Abstract

We are carrying out a survey of 51 poorly studied globular clusters, by means of spectroscopy of ̃20 red giants per cluster. Optical spectra (4600-5800 Å) were obtained with the FORS2@VLT/ESO, at a resolution Delta lambda ̃ 2.5 Å. We are using ETOILE code to derive [Fe/H], T_eff, log g for each star, by finding the best fitting spectrum among a grid of ̃ 2000 stars of the ELODIE library. These parameters represent the initial guess for HALO, which finds [Mg/Fe] values by comparing the observed spectrum to a grid of 4000 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, as well as to find interesting cases for follow-up with high resolution (like M 22, and NGC 5824, for which we found a spread in [Fe/H]).