THE FORMATION OF BARIUM AND CH STARS AND RELATED OBJECTS

We investigate the formation of barium (Ba) and CH stars via binary in teractions. We consider four evolutionary channels for their formation : wind accretion, wind exposure, stable Roche lobe overflow (RLOF), an d common-envelope (CE) ejection, and carry out Monte Carlo simulations . We explore the effects of model parameters, such as a tidal-enhancem ent parameter for stellar wind, a maximum stellar mass for s-processin g, and a minimum core mass for thermal pulsation, on our results. We a lso explore the effects of various assumptions about age, mass-ratio d istribution and wind velocity. Our results show that binary interactio n is successful in explaining the formation of Ba and CH stars. We suc cessfully explain the distribution of orbital periods, the distributio n of mass functions, and the number of observed Ba stars. We also supp ort the views (a) that a tidally enhanced stellar wind exists, (b) tha t thermal pulsation may begin at an earlier phase during the asymptoti c giant branch (AGE) than is usually assumed, and (c) that the maximum stellar mass for s-processing is about 2M(circle dot). We find that t he degree of Ba pollution is strongly correlated with orbital period. The average mass of strong Ba stars is estimated to be 1.8 M(circle do t), and of all Ba stars 1.7 M(circle dot); the average mass for the wh ite dwarf (WD) companions in the Ba-star binaries is estimated to be 0 .60 M(circle dot). The average mass of strong CH stars is estimated to be 1.2 M(circle dot), and the average mass for their WD companions is estimated to be 0.62 M(circle dot). The total number of Ba stars in t he Galaxy brighter than 10th apparent magnitude is estimated to be 600 0, while that of CH stars is much less. We also investigate the format ion of pre-Ba/CH stars, cataclysmic variables, Algols, double degenera tes and symbiotics. Some encouraging results are found, although much work needs to be hone in order to understand fully their formation, es pecially of pre-Ba/CH stars and of symbiotics.