Chemical compositions of four barium stars

Abstract

We obtain abundances of α, iron peak and neutron capture (n-capture) process elements in four Ba stars HD 26886, HD 27271, HD 50082 and HD 98839 based on high resolution, high signal-to-noise spectra. We find that all of these Ba stars are disk stars. Their α and iron peak elements are similar to the solar abundances. The n-capture process elements are overabundant relative to the Sun. In particular, the second peak slow neutron capture process (s-process) elements, Ba and La, are higher than the first peak s-process elements, Y and Zr. Analyzing the abundances of four sample stars, the heavy-element abundances of the strong Ba star HD 50082 are higher than those of other three mild Ba stars. The stellar mass of the strong Ba star HD 50082 is 1.32 (+0.28, ), which is consistent with the average mass of strong Ba stars (1.5 ). For mild Ba star HD 27271, we derive 1.90 (+0.25, ), consistent with the average mass of mild Ba stars (1.9 , with 0.6 white dwarf companion). For mild Ba star HD 26886, the derived 2.78 (+0.75, ) is consistent with the average 2.3 of mild Ba stars with 0.67 companion white dwarfs within the errors. Mass of mild Ba star HD 98839 is high to 3.62 , which inspires more thoughts on the formation of Ba star phenomenon. Using our angular momentum conservation theoretical model of wind accretion of Ba binary systems, we obtain the theoretical heavy-element abundances of Ba stars that best fit our data. The results show that the observed abundances of the typical strong Ba star HD 50082 and the typical mild Ba star HD 27271 are consistent with the theoretical results very well. This suggests that their heavy-element abundances were caused by accreting the ejecta of AGB stars, the progenitors of the present white dwarf companions, through stellar wind. However, wind accretion scenario cannot explain the observed abundance pattern of the mild Ba star HD 26886 with shorter orbital period ( 1263.2 d). The mild Ba star HD 98839 with high mass (up to 3.62 ) and very long orbital period ( 11 000 d) may be either a star with the heavy elements enriched by itself or a “true Ba" star.