Studying chemical enrichment of substructures in the Galaxy (or the distribution of elemental abundances throughout different substructures of the Galaxy) is essential for exploring and understanding the evolution of the Milky Way, in particular its chemical evolution and structure, as well as for testing nucleosynthetic processes and sources of elements. As an important part of the study of chemical composition of the Galactic disc in a broad representation of Galactic substructures, the investigation of open clusters, which also inhabit the Galactic disc, but represent a distinct subpopulation, can give more insight into the enrichment of the disc with different elements and provide additional information about its structure. Moreover, open clusters are an important tool in studying stellar evolution: they are loosely gravitationally bound groups of stars of similar chemical composition and age since they were formed from the same cloud of gas and dust.
This manuscript presents the results of the investigation of parameters and chemical composition of stars in open clusters (OC) inhabiting our Milky Way Galaxy aimed at studying stellar and Galactic evolution. Parameters and abundances of Na, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Y, La, Ce and Nd were determined for nine Main-Sequence stars and three giants in the Hyades open cluster. Giant stars have shown overabundances of sodium, which suggests that thermonuclear (nuclear fusion) reactions of hydrogen burning in the neon-sodium (NeNa) cycle with subsequent ejecting into the upper atmosphere may be occurring.
Radial velocities, atmospheric parameters and chemical compositions of 27 giants belonging to OC, namely Cr 110, Cr 261, NGC 2477, NGC 2506 and NGC 5822, have been determined. Correlations between elemental abundances in cluster stars and metallicity or age of the respective clusters have been examined. The barium excess in OC is confirmed, and higher Ba dispersions in clusters younger than ~ 4 Gyr have been demonstrated. It is also shown that contributions of slow (s-process) or rapid (r-process) neutron-capture processes cannot account for the enrichment in Ba as compared to other neutron-capture elements in OC. For the first time, it is suggested that such an abnormal abundance of Ba can be explained by adding the contribution from the intermediate neutron-capture process (i-process).
Molybdenum abundances have been first determined in stars belonging to 13 OC, namely Berkeley 75, Berkeley 25, Ruprecht 7, Ruprecht 4, Berkeley 73, NGC 6192, NGC 6404, NGC 6583, Collinder 110, Collinder 261, NGC 2477, NGC 2506 and NGC 5822. The abundances of molybdenum in stars inhabiting OC and Galactic disc exhibit similar correlations with metallicities, which suggests a common origin of the investigated stellar populations with a wider scatter of Mo abundances in OC stars. For an extended sample of clusters, no correlation has been found between molybdenum abundance ratios [Mo/Fe] and age of clusters (slope is -0.001 ± 0.010 dex/Gyr).
For all the examined clusters, the relationship between [Mo/Fe] and the Galactocentric radius RGC is represented by a trend line with a slope of 0.018 ± 0.009 dex/kpc; it shows a higher level of statistical significance as compared to previously obtained data, with the slope being different from those obtained for the s- or r-process elements, which is indicative of more complex origin of this element.
The present research yielded the results which can be employed in further studies of stellar evolution, developments in nucleosynthesis, as well as stellar and dynamical Galactic evolution.
