  Elements in the range 37 < Z < 47 provide key information on their formation
process. Several studies have shown that some of these elements are formed by
an r-process, that differs from the main r-process creating europium. Through a
detailed abundance study of Rb - Ag I will show, by comparing these abundances
to those of Ba and Eu, that their formation processes differ. The formation
process of Pd and Ag deviates from the weak/main s-process as well as from the
main r-process. Hence, Pd and Ag - and to some extend Zr - are created by a
second/weak r-process. However, the characteristics and formation site of this
process is not well understood. The abundance ratios of Rb/Zr help constrain
the neutron number density of the formation site, while comparing the Pd and Ag
abundances to yield predictions can provide limitations on the entropy and
electron fraction of the formation environment. This study presents clues on
the second r-process. Furthermore, the formation processes of the heavy
elements might not differ in a clear cut way. Several of these neutron-capture
processes might yield various amounts of heavy elements (e.g. Sr and Ba) at the
same time or metallicity. This could possibly help explain the large
star-to-star abundance scatter for these two elements below [Fe/H]= -2.5.
Knowing their origin is important in the era of large surveys (e.g Gaia-ESO).
Strontium and barium will, limited by resolution and signal-to-noise ratio, be
the only detectable heavy elements in the most metal-poor stars. Hence, they
will, depending on metallicity, be the main tracers of the weak and main
s-/r-processes. Understanding the effects of stellar parameters, synthetic
spectrum codes, model atmospheres, and NLTE on the Sr abundances are crucial to
describe the chemical evolution of our Galaxy. I will present these effects for
Sr.
