The r-process is responsible for the synthesis of roughly half of the elements heavier than Fe in the solar system, however the nucleosynthesis of these elements is still not fully understood. High resolution spectra show that both r-rich and r-poor metal-poor stars have robust chemical abundance patterns in the region of Z between 60 and 70, often referred to as the universality of the heavy r-process. Outside this range of Z, however, clear variations in the abundance patterns are seen between r-rich and r-poor stars, typically in the lighter heavy elements, and in the actinide elements. Such abundance pattern variations could only occur if the physical conditions vary during the r-process event, or if multiple different formation sites contribute. To understand the physical mechanisms and production sites of r-process elements in the early Universe, we need detailed chemical abundance patterns for a large sample of metal-poor stars, in order to compare them with the ones predicted by theoretical nucleosynthesis models. Thanks to the high quality of our spectra, we could measure the chemical abundances of 9 heavy elements up to Eu (Ru, Ag, Ba, La, Ce, Pr, Nd, Sm, Eu) in a sample of 52 very metal-poor stars. The presented work will be focused on exploring the impact of the r-process on heavy elements in a sample of r-rich and r-poor metal-poor stars.
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