An abundance analysis of the single-lined spectroscopic binaries with barium stars-like orbital elements

Abstract

Detailed abundance analyses have been car- ried out for 17 single-lined binaries (giants and dwarfs) with orbital elements and mass functions similar to those of barium stars, using high-dispersion CCD spectra and model atmospheres. All these binary systems contain an unseen low-mass component, presumably, a white dwarf. A mild enhancement (+0:1 0:25 dex) of the averaged s- process elements abundances has been found only for two stars. The heavy-element overabundances in these stars are much less marked than those of the classical barium stars having similar orbital periods. We have concluded that the existence of a white dwarf (WD) companion in binary systems with barium star like characteristics is not sucient to produce a strong barium star. However, ve of the analyzed giants show a signicant enhancement (0:2 0:3 dex) of barium. The analysis indicates that a main sequence companion has not a signicant influ- ence (due to tidal mixing, as has been sometimes sug- gested) on the internal structure (chemical composition) of the primary star. Since barium enhanced giants occupy a place on the (eccentricity-orbital period) plane similar to BaII stars we have concluded that a mild barium enhance- ment in these stars is due to mass transfer from the com- panion during its late phases of evolution. Thus it seems likely that all giants (primaries) in barium star like binary systems with WD component have chemical peculiarities (very slight in some cases) depending, apparently, on the eciency of mass transfer in a specic binary system. The signicant enhancement of heavy elements in the atmo- spheres of two radial velocity non-variable barium stars