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 .