Cobalt and copper abundances in 56 Galactic bulge red giants
  The Milky Way bulge is an important tracer of the early formation and
chemical enrichment of the Galaxy. The abundances of different iron-peak
elements in field bulge stars can give information on the nucleosynthesis
processes that took place in the earliest supernovae. Cobalt (Z=27) and copper
(Z=29) are particularly interesting.We aim to identify the nucleosynthesis
processes responsible for the formation of the iron-peak elements Co and Cu.
Methods. We derived abundances of the iron-peak elements cobalt and copper in
56 bulge giants, 13 of which were red clump stars. High-resolution spectra were
obtained using FLAMES-UVES at the ESO Very Large Telescope by our group in
2000-2002, which appears to be the highest quality sample of high-resolution
data on bulge red giants obtained in the literature to date. Over the years we
have derived the abundances of C, N, O, Na, Al, Mg; the iron-group elements Mn
and Zn; and neutron-capture elements. In the present work we derive abundances
of the iron-peak elements cobalt and copper. We also compute chemodynamical
evolution models to interpret the observed behaviour of these elements as a
function of iron. The sample stars show mean values of [Co/Fe]~0.0 at all
metallicities, and [Cu/Fe]~0.0 for [Fe/H]>-0.8 and decreasing towards lower
metallicities with a behaviour of a secondary element. We conclude that [Co/Fe]
varies in lockstep with [Fe/H], which indicates that it should be produced in
the alpha-rich freezeout mechanism in massive stars. Instead [Cu/Fe] follows
the behaviour of a secondary element towards lower metallicities, indicating
its production in the weak s-process nucleosynthesis in He-burning and later
stages. The chemodynamical models presented here confirm the behaviour of these
two elements (i.e. [Co/Fe] vs. [Fe/H]~constant and [Cu/Fe] decreasing with
decreasing metallicities).
