The problem of n-capture nucleosynthesis in intermediate-mass stars during the thermal instabilities of the He shell is reanalyzed in the light of an updated set of cross sections for n-captures and of reaction rates for alpha reactions. The reaction network used in the calculations is sketched and inserted into models of thermal phases derived from new evolutionary computations for a Population II star developing an H-exhausted core of 1.07 solar mass and from published data on Population I He-shell instabilities. The computations invariably lead to strongly nonsolar distributions of s-elements. In the majority of cases, high neutron densities are found, implying the saturation of many s-branches and the production of r-isotopes. The reaction Ne-22 (alpha, n) Mg-25 probably cannot give rise to a solar distribution of s-nuclei.
Are s-elements really produced during thermal pulses in intermediate-mass stars?
BUSSO, Maurizio Maria;
1988
Abstract
The problem of n-capture nucleosynthesis in intermediate-mass stars during the thermal instabilities of the He shell is reanalyzed in the light of an updated set of cross sections for n-captures and of reaction rates for alpha reactions. The reaction network used in the calculations is sketched and inserted into models of thermal phases derived from new evolutionary computations for a Population II star developing an H-exhausted core of 1.07 solar mass and from published data on Population I He-shell instabilities. The computations invariably lead to strongly nonsolar distributions of s-elements. In the majority of cases, high neutron densities are found, implying the saturation of many s-branches and the production of r-isotopes. The reaction Ne-22 (alpha, n) Mg-25 probably cannot give rise to a solar distribution of s-nuclei.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
