Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26as..113..299m&link_type=abstract
Astronomy and Astrophysics Supplement, v.113, p.299
Astronomy and Astrophysics
Astrophysics
28
Stars: Abundances, Galaxy: Abundances, Galaxy: Globular Clusters
Scientific paper
We present a large dataset consisting of giants in the field, and in open and globular clusters. A total of 122 giants were observed in the fields of 8 open clusters. A total of 342 giants were observed in the fields of 25 globular clusters. A total of 36 field stars with well known abundances and luminosities were also observed. Radial velocities are determined for most giants, some of which have no photometry available. We have analyzed several spectral features in order to define a grid that will allow the determination of metal abundances for halo and bulge giants. The errors involved in the determination of radial velocities and [Fe/H] are carefully examined. We find that field and open cluster stars on one side, and globular cluster giants on the other side, do not follow the same calibration. This is possibly due to enhanced [α/Fe] abundances in globular clusters. Therefore, we have defined a calibration based only on globular cluster giants, valid from [Fe/H]=-2.0 to +0.5. This calibration is carried out with the purpose of measuring metallicities for bulge and halo giants, with the underlying assumption that the abundance ratios of the relevant elements relative to iron are similar to the calibrating stars. Adopting as standards the globular clusters NGC 288, NGC 362, NGC 1851, NGC 6356, NGC 6624, 47 Tuc, M 4 , M 3, and M 22 we derive metallicities for globular clusters with less well known compositions, like M 28, and NGC 6637. In particular, we confirm a low metallicity for M 28 ([Fe/H]=-1.35+/-0.2), a cluster that has a disk orbit.
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