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

Frischknecht, Urs; Hirschi, Raphael; Pignatari, Marco; Maeder, André; Meynet, George; Chiappini, Cristina; Thielemann, Friedrich-Karl; Rauscher, Thomas; Georgy, Cyril; Ekström, Sylvia

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Urs Frischknecht

Marco Pignatari

André Maeder

George Meynet

Cristina Chiappini

Friedrich-Karl Thielemann

Thomas Rauscher

Cyril Georgy

Sylvia Ekström


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 15–40?M? 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 neutron-to-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.

Journal Article Type Article
Acceptance Date Nov 18, 2015
Online Publication Date Dec 28, 2015
Publication Date Feb 21, 2016
Publicly Available Date May 26, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 456
Issue 2
Pages 1803 - 1825
Keywords stars:abundances; stars:chemically peculiar; stars:massive; stars:population II; stars:rotation; galaxy:abundances
Publisher URL


R Hirschi - sprocess production in rotating massive stars at solar and low metallicities.pdf (3.4 Mb)

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