Blue straggler stars in galactic open clusters

Blue straggler stars (BSS) were originally identified in the color-magnitude diagram (CMD) of the globular cluster M3, where they defined an extension of the cluster main sequence, blueward and above the turnoff (TO). Among the variety of objects that populate stellar clusters, BSS are surely between those still presenting many puzzles to astronomers since they are considered crucial probes for the study of the complex interaction between stellar evolution and stellar dynamics. Further, their presence poses a challenge for the standard single-star evolution theory, since stars with masses higher than that of the cluster TO should have evolved into the white dwarf regime long ago and, besides, the major formation scenarios for BSS involve stellar interactions. At present, these exotic stars have been largely identified in different stellar systems, such as globular clusters (GCs), dwarf galaxies, open clusters (OCs), and even in the field populations of the Milky Way. In particular, available catalogs of BSS in OCs are purely based on photometric criteria, namely only the location of a given star in the CMD dictates its BS nature. Nevertheless, systematic investigations of the properties of galactic OCs are hampered by the inhomogeneity of the data available by the date of the catalogs were published, and consequently, the BSS reported in this catalog are mostly of uncertain membership. Thus, while useful, these compilations are not reliable enough to allow the derivation of statistical properties of BSS. The principal aim of this thesis was to create a catalog of BSs in OCs based on the astrometric solutions of Gaia DR2 and not only on photometric criteria. In addition, we have searched also for possible yellow stragglers stars (YSS) i.e possible evolved BSS. Finally, we have complement Gaia DR2 data with multi-epoch spectroscopic data from FLAMES, which allowed us to have a closer look at the BS population in four OCs with very different properties: age, metallicity, mass, and location in the MW disk.