A CHEMICAL ABUNDANCE STUDY OF 10 OPEN CLUSTERS BASED ON WIYN-HYDRA SPECTROSCOPY

Abstract

We present a detailed chemical abundance study of evolved stars in 10 open\nclusters based on Hydra multi-object echelle spectra obtained with the WIYN\n3.5m telescope. From an analysis of both equivalent widths and spectrum\nsynthesis, abundances have been determined for the elements Fe, Na, O, Mg, Si,\nCa, Ti, Ni, Zr, and for two of the 10 clusters, Al and Cr. To our knowledge,\nthis is the first detailed abundance analysis for clusters NGC 1245, NGC 2194,\nNGC 2355 and NGC 2425. These 10 clusters were selected for analysis because\nthey span a Galactocentric distance range Rgc~9-13 kpc, the approximate\nlocation of the transition between the inner and outer disk. Combined with\ncluster samples from our previous work and those of other studies in the\nliterature, we explore abundance trends as a function of cluster Rgc, age, and\n[Fe/H]. The [Fe/H] distribution appears to decrease with increasing Rgc to a\ndistance of ~12 kpc, and then flattens to a roughly constant value in the outer\ndisk. Cluster average element [X/Fe] ratios appear to be independent of Rgc,\nalthough the picture for [O/Fe] is more more complicated by a clear trend of\n[O/Fe] with [Fe/H] and sample incompleteness. Other than oxygen, no other\nelement [X/Fe] exhibits a clear trend with [Fe/H]; likewise, there does not\nappear to be any strong correlation between abundance and cluster age. We\ndivided clusters into different age bins to explore temporal variations in the\nradial element distributions. The radial metallicity gradient appears to have\nflattened slightly as a function of time, as found by other studies. There is\nalso indication that the transition from the inner disk to the outer disk\noccurs at different Galactocentric radii for different age bins. (Abridged.)\n