SPECIFIC FEATURES OF THE ENRICHMENT OF METAL-POOR STARS WITH NEUTRON-CAPTURE (R-PROCESS) ELEMENTS

In contrast to stars with near-solar metallicity (Galactic disk stars), metal-deficient stars show an abundance scatter of up to 3 dex in the enrichment with neutron-capture elements, in particular the r-process elements. The reasons of such a large variation in the in the r-process nucleosynthesis is currently matter of debate. Possible scenarios could be the presence of various r-process stellar and mechanisms in the early unevenly mixed Galaxy, as well as different stellar origin, either galactic or extragalactic, that reflect entering the Galaxy after the capture or coalescence of both individual stars and more complex stellar associations and star formations. In order to study differences in the enrichment with the r-process elements, we selected 20 metal-deficient stars, the spectra of which were collected in the UVES/VLT archive. We employed earlier determined atmospheric parameters to calculate the abundances of about 20 neutron-capture elements via the synthetic spectrum method, taking into account the hyperfine structure for a number of elements. We performed an analysis of the enrichment with the r-process elements grounded on multiple levels of enrichment intensity – namely, limited r-process, r-I and r-II – and the arrangement of stars by their belonging to different populations of the Galaxy, based on the stars’ spatial velocity components.