Volume 458, Number 3, November II 2006
|Page(s)||777 - 788|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||12 September 2006|
Medium resolution spectroscopy in ω Centauri: abundances of 400 subgiant and turn-off region stars
Sternwarte der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
2 Astronomisches Institut der Universität Basel, Venusstrasse 7, 4102 Binningen, Switzerland e-mail: firstname.lastname@example.org
3 Universidad de Concepción, Departamento de Física, Casilla 106-C, Concepción, Chile
Accepted: 29 June 2006
Medium resolution spectra of more than 400 subgiant and turn-off region stars in ω Centauri were analysed. The observations were performed at the VLT/Paranal with FORS2/MXU. In order to determine the metallicities of the sample stars, we defined a set of line indices (mostly iron) adjusted to the resolution of our spectra. The indices as determined for ω Cen were then compared to line indices from stars in the chemically homogeneous globular cluster M 55, in addition to standard stars and synthetic spectra. The uncertainties in the derived metallicities are of the order of ±. Our study confirms the large variations in iron abundances found on the giant branch in earlier studies (Fe/H dex). In addition, we studied the α-element and CN/CH abundances. Stars of different metallicity groups not only show distinct ages (Hilker et al. 2004, A&A, 422, L9), but also different behaviours in their relative abundances. The α abundances increase smoothly with increasing metallicity resulting in a flat [ α/Fe] ratio over the whole observed metallicity range. The combined CN+CH abundance increases smoothly with increasing iron abundance. The most metal-rich stars are CN-enriched. In a CN vs. CH plot, though, the individual abundances divide into CN- and CH-rich branches. The large abundance variations observed in our sample of (unevolved) subgiant branch stars most probably have their origin in the pre-enriched material rather than in internal mixing effects. Together with the age spread of the different sub-populations, our findings favour the formation of ω Centauri within a more massive progenitor.
Key words: stars: abundances / Galaxy: globular clusters: individual: ω Cen / galaxies: dwarf / galaxies: nuclei
© ESO, 2006
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.