Abundances in Turn-off Stars in the Old, Metal-Rich Open Cluster, NGC
  6791
  Open clusters have long been used to illuminate both stellar evolution and
Galactic evolution. The oldest clusters, though rather rare, can reveal the
chemical and nucleosynthetic processes early in the history of the Galaxy. We
have studied two turn-off stars in the old, metal-rich open cluster, NGC 6791.
The Keck + HIRES spectra have a resolution of 45,000 and signal-to-noise ratios
of 40 per pixel. We confirm the high value for [Fe/H] finding +0.30 $\pm$0.08,
in agreement with earlier results from evolved stars in other parts of the HR
diagram. We have also determined abundances for Na, Si, Ca, Ti, Cr, Ni, Y and
Ba. These are compared to a sample of old, metal-rich field stars. With the
probable exception of enhanced Ni in the cluster stars, the field and cluster
stars show similar abundances of the elements. Model predictions show that the
Ni enhancement could result from enrichment of the pre-cluster gas by SN Ia.
Orbital evidence indicates that NGC 6791 could have originated near the inner
regions of the Galaxy where the metallicity is generally higher than it is in
the disk or halo. Subsequent perturbations and migrations may have resulted in
its current heliocentric distance of 4 kpc and 1 kpc above the Galactic plane.
