New Neutron-Capture Measurements in 23 Open Clusters. I. The R-Process
  Neutron-capture elements, those with Z > 35, are the least well-understood in
terms of nucleosynthesis and formation environments. The rapid neutron-capture,
or r-process, elements are formed in the environments and/or remnants of
massive stars, while the slow neutron-capture, or s-process, elements are
primarily formed in low-mass AGB stars. These elements can provide much
information about Galactic star formation and enrichment, but observational
data is limited. We have assembled a sample of 68 stars in 23 open clusters
that we use to probe abundance trends for six neutron-capture elements (Eu, Gd,
Dy, Mo, Pr, and Nd) with cluster age and location in the disk of the Galaxy. In
order to keep our analysis as homogenous as possible, we use an automated
synthesis fitting program, which also enables us to measure multiple (3-10)
lines for each element. We find that the pure r-process elements (Eu, Gd, and
Dy) have positive trends with increasing cluster age, while the mixed r- and s-
process elements (Mo, Pr, and Nd) have insignificant trends consistent with
zero. Pr, Nd, Eu, Gd, and Dy have similar, slight (though mostly statistically
significant) gradients of ~0.04 dex/kpc. The mixed elements also appear to have
nonlinear relationships with Galactocentric radius.
