Of Agb Star He Shell Nucleosynthesis Of Heavy Elements

Adopting the branched s-process path and the new neutron cross cection, we calculate the s-process nucleosynthesis for$3M0 AGB stars of different metallicities, based on the nucleosynthesis scenario given by Busso et al. (1999) and Liang et al. (2000). The neutron irradiation is assumed to derive primarily by the reaction 13C(a , n) I60 with a minor contribution from the marginal burning of 22Ne through the channel 22Ne(a n)23Mg in the final, high temprature phase of each flash. And we considered the influence of the various parameters such as the initial core mass, the envelope mass, the mass-loss rate, the overlap factor and the delution factor etc., and we vary their value with the pulse number. We spanned the mettalicity from [Fe/H]=0. 4 to [Fe/H]=-3. 2. The abundance of feed nuclei 6Fe of s-process is proportional to metalicity. The amount of 13C burnt per pulse is the same as the standard modal of Gallino et al. (1998). A detailed analysis of the obtained abundance distribution is presented. We separate the main s-process component into two parts, s, (88A138, A is the mass number of the nuclei) and smh (138A209), to discuss. The results indicate that the distribution of sBl component varies as a function of metallicity, as compared to the relatively stable pattern of s component. Moreover, after we have the abundances of nuclei divided by the corresponding solar s-main abundance, some very interesting characters are indicated:1. The abundance distributions of the sh component for the bulk ofisotopes 140A204 are strongly similar to the solar s-main pattern at any metallicity.2. The abundance distributions of the sBl component part with 92 A132 are nearly similar to the solar pattern at any metallicity.Thus the cumulative consequence of Galactic chemical evolution starting from low metallicity AGB stars, namely, the average abundance patterns of sBh part with 140A204 (or the snl component part with 92A132) in different metal conditions, should be similar (ornearly similar) to the corresponding solar s-Bajn component. Consequently the distributions of the corresponding solar s,h component is typical and can serve as a standard pattern in investigating the abundance distribution of neutron capture elements at any metallicity. And the solar s, component can serve as a rough standard pattern.S-process nucleosynthesis may be a useful constraint for the evolution and convection in massive stars. Adopting single pulse neutron exposure 22Ne(a,n)2DMg and the updated neutron cross section, making use of the core helium burning model of the single neutron exposure theory, we calculate the s-process nucleosynthesis in massive stars at different mettalicity and compare the results with the solar s-weak component. We find that the abundance distributions of the s. component is not similar to the solar s-weak pattern, so the solar s-weak component can not be take as the standard pattern.