The Open Cluster Chemical Analysis and Mapping Survey: Local Galactic Metallicity Gradient with APOGEE Using SDSS DR10

The Open Cluster Chemical Analysis and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based data set for hundreds of open clusters, and constrain key Galactic dynamical and chemical parameters from this sample. This first contribution from the OCCAM survey presents analysis of 141 members stars in 28 open clusters with high-resolution metallicities derived from a large uniform sample collected as part of the Sloan Digital Sky Survey III/Apache Point Observatory Galactic Evolution Experiment. This sample includes the first high-resolution metallicity measurements for 22 open clusters. With this largest ever uniformly observed sample of open cluster stars we investigate the Galactic disk gradients of both [M/H] and [α/M]. We find basically no gradient in [α/M] across 7.9 kpc <= R _GC <= 14.5 kpc, but [M/H] does show a gradient for R _GC < 10 kpc and a significant flattening beyond R _GC = 10 kpc. In particular, whereas fitting a single linear trend yields an [M/H] gradient of -0.09 ± 0.03 dex kpc^-1—similar to previously measure gradients inside 13 kpc—by independently fitting inside and outside 10 kpc separately we find a significantly steeper gradient near the Sun (7.9 <= R _GC <= 10) than previously found (-0.20 ± 0.08 dex kpc^-1) and a nearly flat trend beyond 10 kpc (-0.02 ± 0.09 dex kpc^-1).