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        S-process production in rotating massive stars at solar and low metallicities

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        Author
        Frischknecht, Urs
        Hirschi, Raphael
        Pignatari, Marco
        Maeder, André
        Meynet, George
        Chiappini, Cristina
        Thielemann, Friedrich Karl
        Rauscher, Thomas
        Georgy, Cyril
        Ekström, Sylvia
        Attention
        2299/18783
        Abstract
        Rotation was shown to have a strong impact on the structure and light element nucleosynthesis in massive stars. In particular, models including rotation can reproduce the primary nitrogen observed in halo extremely metal poor (EMP) stars. Additional exploratory models showed that rotation may enhance s-process production at low metallicity. Here we present a large grid of massive star models including rotation and a full s-process network to study the impact of rotation on the weak s-process.We explore the possibility of producing significant amounts of elements beyond the strontium peak, which is where the weak s-process usually stops.We used the Geneva stellar evolution code coupled to an enlarged reaction network with 737 nuclear species up to bismuth to calculate 15-40M⊙ models at four metallicities (Z = 0.014, 10-3, 10-5 and 10-7) from the main sequence up to the end of oxygen burning. We confirm that rotation-induced mixing between the convective H-shell and He-core enables an important production of primary 14N and 22Ne and s-process at low metallicity. At low metallicity, even though the production is still limited by the initial number of iron seeds, rotation enhances the s-process production, even for isotopes heavier than strontium, by increasing the neutronto- seed ratio. The increase in this ratio is a direct consequence of the primary production of 22Ne. Despite nuclear uncertainties affecting the s-process production and stellar uncertainties affecting the rotation-induced mixing, our results show a robust production of s-process at low metallicity when rotation is taken into account. Considering models with a distribution of initial rotation rates enables us to reproduce the observed large range of the [Sr/Ba] ratios in (carbon-enhanced and normal) EMP stars.
        Publication date
        2015-12-28
        Published in
        Monthly Notices of the Royal Astronomical Society
        Published version
        https://doi.org/10.1093/mnras/stv2723
        Other links
        http://hdl.handle.net/2299/18783
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