Comprehensive abundance analysis of red giants in the open clusters Stock 2, NGC 2168, 6475, 6991, and 7762
We have analysed high dispersion echelle spectra $R 60000$ of red giant members of five open clusters to derive abundances for many elements from Na to Eu. The [Fe/H] values are 0.06\pm0.03$ for Stock 2, 0.11\pm0.03$ for NGC 2168, 0.01\pm0.03$ for NGC 6475, $0.00\pm0.03$ for NGC 6991 and 0.07\pm0.03$ for NGC 7662. Sodium is enriched in the giants relative to the abundance expected of main sequence stars of the same metallicity. This enrichment of [Na/Fe] by about +0.25$ attributed to the first dredge up is discussed in the light of theoretical predictions and recently published abundance determinations. Abundance ratios [El/Fe] for other elements are with very few exceptions equal to those of field giants and dwarfs, i.e. [El/Fe] \simeq 0.00$ for [Fe/H] \sim 0.0$ An exception is the overabundance of La, Ce, Nd and Sm in NGC 6991 but this is consistent with our previous demonstration that the abundances of these $s$ process products vary by about \pm0.2$ among clusters of the same [Fe/H] a variation found also among field giants and dwarfs.
Monthly Notices of the Royal Astronomical Society