The Effect Of Mass Accretion On Elemental Abundances Of Metal-Poor Extrinsic AGB Stars

On the basis of the parametric method of s-process nucleosynthesis,considering the heavy-element overabundance of the extrinsic AGB stars may come from mass accretion in a binary system,and the binary star interactions increase the mass loss of the main companions,the mass loss does play a determinative role in the AGB evolution,we suggest a mass accretion parametric model in a binary system for the extrinsic AGB stars:Adopt the mass transfer rate for stable RLOF,and fit the surface elemental abundances of 10 metal-poor stars through successive pulses transferring with mixing.As a result,we get a good fit to the observed abundances whether the reaction branchings are taken into account or not.When the binary mass accretion is included,the overlap factor of s-process in the main companions lies between 0.100 and 0.850,The neutron exposure per pulse lies between 0.425 and 0.769 mb? 1,The parameter R1 /RL which determines RLOF lies between 1.430 and 4.435.The production of lead-rich stars has the satisfaction of M i≤1.45M,smaller dredge-up extent and larger R1 / RL 1;and the no lead stars may due to main companions with M i≥2.00M,larger dredge-up extent and smaller R1 / RL 1.By comparison of the main companions initial Roche-lobe radii of the extrinsic S stars with those of s+r stars in this paper,the former is smaller than that of the latter.The initial-final mass relation of the main companion steepens with the metallicity decreases,this supports the formation of s+r stars via AGB supernovae or AIC.