The Mass Accretion And Yields Of R-process In The S+r Stars

The origin of the s+r stars is one of the most important issues in the field of Astronomy. They may originate from a binary system. Large amounts of Carbon and s-process elements is produced during the AGB evolution of the main star. The secondary exhibits overabundance of carbon and s-process elements by accreting material enriched in carbon and s-process elements from the main one. Due to the low mass-loss efficiency, the final mass of the AGB star at low metallicity will reach the Chandrasekhar mass and significant amount of r-process material may be produced out of the AIC or type -1.5 supernova.We suggest that the s+r stars may originate from a former 3-5 M companion in a binary system. We discuss the law of the r-process mass accretion by taking account of different models of the s-process mass accretion, different assumptions of the r-process mass transfer and the strong correlation between the component coefficients of the s-process and r-process.The calculation shows that the material of the r-process the secondary received becomes less with the distance of the binary becomes wider. This is significant evidence for the formation of the AIC or type-1.5 supernova. Like the s-process mass accretion, an enhancement factor f takes place in the r-process mass accretion too. While the distance of the binary becomes wider, the enhancement factor becomes larger. Considering the gravitational effects, the reason of the factor fr getting bigger can be explained by the reducing of the velocity of the wind (when it reaches the secondary) while the distance of the binary become wider.Using the energy conservation law and Bondi accretion law, we deduced the initial velocity of the wind to be about 7000km/s. According to our results the mass of Eu ejected by the main star is about 10-8 M out of the AIC or type -1.5 supernova.