A chemical abundance study of red giants in open clusters NGC 2204 and NGC 2243

Abstract

Detailed element abundances have been determined for 10-13 stars each in the open clusters (OCs) NGC 2204 and NGC 2243 based on Hydra multi-object echelle spectra obtained with the CTIO 4 m telescope. We have found average cluster metallicities of [Fe/H] = ?0.23 ± 0.04 and ?0.42 ± 0.05 for NGC 2204 and NGC 2243, respectively, from an equivalent width analysis. NGC 2243 is themostmetal-poor cluster at its Galactocentric radius and is one of the most metal-poor OCs currently known. These two clusters lie ∼ 1 kpc below the Galactic plane; it is therefore worthwhile to compare their abundance patterns to those of clusters both closer to and further from the plane. To that end, we combined the results of the current study with those of clusters from our previous work as well as from the literature. To minimize systematic differences between different studies, element abundances of many outer disk OCs as well as thin and thick disk field stars have been placed on our abundance scale. Plots of [X/Fe] versus [Fe/H] for NGC 2204, NGC 2243, other clusters from the literature, and thin and thick disk field stars show NGC 2204 and NGC 2243 to have element abundance patterns comparable to those of other clusters regardless of distance from the plane or center of the Galaxy. Similarly, no individual cluster or group of clusters far from the Galactic mid-plane can be identified as belonging to the thick disk based on their abundance patterns. © 2011. The American Astronomical Society. All rights reserved.