Abundances of Red Giants in the Old Open Cluster Collinder 261

Abstract

We present an analysis of high-dispersion echelle spectra of four giant stars in the 8 Gyr open cluster Cr 261 obtained with the Cerro Tololo Inter-American Observatory's 4 m telescope. Abundances were determined relative to the bright, slightly metal-poor disk giant Arcturus. Cr 261 is found to have a mean [Fe/H] = -0.22 ± 0.05 (mean error). Oxygen abundances, determined from the forbidden [O I] lines, show roughly solar or slightly depleted abundance ratios. The α-elements Mg, Ca, and Ti also show scaled solar abundance ratios, with suggestions that the Si abundance is slightly enhanced. The odd-Z elements Na and Al are significantly enhanced relative to scaled solar abundances. The abundance results for Cr 261 are compared with those from high-dispersion studies of other old open clusters in the literature, which, overall, show similar behavior in all these elements. None of the abundance ratios show significant trends with overall cluster [Fe/H] or with cluster age.