ABUNDANCES OF RED GIANTS IN OLD OPEN CLUSTERS. IV. NGC 1817, NGC 1883, NGC 2141, AND NGC 2158

We present an analysis of high-dispersion echelle spectra of seven giant stars in the ∼1-2 Gyr old open clusters NGC 1817, NGC 1883, NGC 2141, and NGC 2158. Abundances were determined relative to the bright, mildly metal-poor disk giant Arcturus. NGC 1817, NGC 1883, NGC 2141, and NGC 2158 are found to have a mean [Fe/H] = -0.07 ± 0.04, -0.01 ± 0.01, +0.00 ± 0.16, and -0.03 ± 0.14 (s.d.), respectively. All four clusters show modest (∼0.1 dex) enhancements of Na and Si, and scaled solar abundances of Al and Mg, while [O/Fe] ∼ -0.15 dex. [Ca/Fe] and [Ti/Fe] values are slightly subsolar in all four clusters, but this may be due to a systematic effect. Given that all four of these clusters are located at R gc > 10 kpc in the disk, and barring any systematic effects, our results imply that any abrupt transition in abundance in the Galactic disk occurs beyond R gc ∼ 13 kpc.