摘要：Context. Globular clusters trace the formation and evolution of the
Milky Way and surrounding galaxies, and outline their chemical enrichment history. To
accomplish these tasks it is important to have large samples of clusters with homogeneous
data and analysis to derive kinematics, chemical abundances, ages and locations.
Aims. We obtain homogeneous metallicities and α-element enhancement for
51 Galactic bulge, disc, and halo globular clusters that are among the most distant and/or
highly reddened in the Galaxy’s globular cluster system. We also provide membership
selection based on stellar radial velocities and atmospheric parameters. The implications
of our results are discussed.
Methods. We observed R ~ 2000 spectra in the wavelength interval
456–586 nm for over 800 red giant stars in 51 Galactic globular clusters. We applied full
spectrum fitting with the code ETOILE together with libraries of observed and synthetic
spectra. We compared the mean abundances of all clusters with previous work and with field
stars. We used the relation between mean metallicity and horizontal branch morphology
defined by all clusters to select outliers for discussion.
Results. [Fe/H], [Mg/Fe], and [α/Fe] were derived in a
consistent way for almost one-third of all Galactic globular clusters. We find our
metallicities are comparable to those derived from high-resolution data to within
σ = 0.08
dex over the interval −2.5<
[Fe/H] < 0.0. Furthermore,
a comparison of previous metallicity scales with our values yields σ< 0.16 dex. We also
find that the distribution of [Mg/Fe] and [α/Fe] with [Fe/H] for the 51 clusters follows the
general trend exhibited by field stars. It is the first time that the following clusters
have been included in a large sample of homogeneous stellar spectroscopic observations and
metallicity derivation: BH 176, Djorg 2, Pal 10, NGC 6426, Lynga 7, and Terzan 8. In
particular, only photometric metallicities were available previously for the first three
clusters, and the available metallicity for NGC 6426 was based on integrated spectroscopy
and photometry. Two other clusters, HP 1 and NGC 6558, are confirmed as candidates for the
oldest globular clusters in the Milky Way.
Conclusions. Stellar spectroscopy in the visible at R ~ 2000 for a large
sample of globular clusters is a robust and efficient way to trace the chemical evolution
of the host galaxy and to detect interesting objects for follow-up at higher resolution
and with forthcoming giant telescopes. The technique used here can also be applied to
globular cluster systems in nearby galaxies with current instruments and to distant
galaxies with the advent of ELTs.
关键词：stars: abundances;stars: kinematics and dynamics;stars: Population
II;Galaxy: stellar content;Galaxy: evolution;globular
clusters: general
