Homogeneous metallicities and radial velocities for Galactic globular clusters

First CaT metallicities for twenty clusters^⋆,⋆⋆

¹ European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
e-mail: isaviane@eso.org
² Research School of Astronomy & Astrophysics, Australian National University, Mt Stromlo Observatory, via Cotter Rd, Weston, ACT 2611, Australia
e-mail: gdc@mso.anu.edu.au
³ INAF, Osservatorio Astronomico di Padova, vicolo Osservatorio 5, 35122 Padova, Italy
e-mail: enrico.held@oapd.inaf.it
⁴ Royal Observatory, Avenue Circulaire 3, 1180 Bruxelles, Belgium
e-mail: M.Gullieuszik@oma.be
⁵ University of Sao Paulo, Rua do Matao 1226, Sao Paulo 05508-900, Brazil
e-mail: barbuy@astro.iag.usp.br
⁶ University of Padova, vicolo Osservatorio 5, 35122 Padova, Italy
e-mail: sergio.ortolani@unipd.it
⁷ INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
e-mail: veronica@arcetri.astro.it

Received: 22 September 2011
Accepted: 30 January 2012

Abstract

Well determined radial velocities and abundances are essential for analyzing the properties of the globular cluster system of the Milky Way. However more than 50% of these clusters have no spectroscopic measure of their metallicity. In this context, this work provides new radial velocities and abundances for twenty Milky Way globular clusters which lack or have poorly known values for these quantities. The radial velocities and abundances are derived from spectra obtained at the Ca ii triplet using the FORS2 imager and spectrograph at the VLT, calibrated with spectra of red giants in a number of clusters with well determined abundances. For about half of the clusters in our sample we present significant revisions of the existing velocities or abundances, or both. We also confirm the existence of a sizable abundance spread in the globular cluster M 54, which lies at the center of the Sagittarius dwarf galaxy. In addition evidence is provided for the existence of a small intrinsic internal abundance spread (σ[Fe/H]_int ≈ 0.11 − 0.14 dex, similar to that of M 54) in the luminous distant globular cluster NGC 5824. This cluster thus joins the small number of Galactic globular clusters known to possess internal metallicity ([Fe/H]) spreads.