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Nuclear reactions drive stellar evolution and contribute to stellar and galactic chemical abundances. New determinations of the nuclear reaction rates in key fusion reactions of stellar evolution are now available, paving the way for improved stellar model predictions. We explore the impact of new $ C+^ \!C$ reaction rates in massive star evolution, structure, and nucleosynthesis at carbon ignition and during the core carbon-burning phase. We analyse the consequences for stars of different masses including rotation-induced mixing. We computed a grid of massive stars from 8 to 30 M$_ at solar metallicity using the stellar evolution code GENEC, and including the new reaction rates. We explored the results using three different references for the rates, with or without rotation. We studied the effect in terms of evolution, structure, and the critical mass limit between intermediate and massive stars. We explored the consequences for heavy-element nucleosynthesis during the core carbon-burning phase by means of a one-zone nucleosynthesis code. We confirm the significant impact of using the recent nuclear reaction rates following the fusion suppression hypothesis at deep sub-barrier energies (hindrance hypothesis) as well as the mass-dependent effect of a resonance at 2.14 MeV with dominant feeding of the alpha exit channel of $ C+^ \!C$ fusion reaction. This impacts the characteristics of the core of stars from the C-ignition and during the entire core C-burning phase (temperature and density, lifetime, size, convective or radiative core). The change in nuclear reaction rates modifies the central nucleosynthesis of the stars during the core-carbon burning phase, resulting in an underproduction of s-process elements, especially when including the rotation-induced mixing that amplifies the effects. The correct and accurate determination of the nuclear reaction rates, especially with the existence and location of resonances, impacts stellar evolution in many respects, affecting models' predictions. The choice of the nuclear reaction rates reference for the $ C+^ C$ fusion reaction significantly changes the behaviour of the core during the carbon-burning phase, and consequently drives changes in the nucleosynthesis and end-of-life of stars. This choice needs, then, to be made carefully in order to interpret stellar evolution from the super asymptotic giant branch phase and its massive white dwarf remnants to the core-collapse supernovae of massive stars.
Nuclear reactions drive stellar evolution and contribute to stellar and galactic chemical abundances. New determinations of the nuclear reaction rates in key fusion reactions of stellar evolution are now available, paving the way for improved stellar model predictions. We explore the impact of new $ C+^ \!C$ reaction rates in massive star evolution, structure, and nucleosynthesis at carbon ignition and during the core carbon-burning phase. We analyse the consequences for stars of different masses including rotation-induced mixing. We computed a grid of massive stars from 8 to 30 M$_ at solar metallicity using the stellar evolution code GENEC, and including the new reaction rates. We explored the results using three different references for the rates, with or without rotation. We studied the effect in terms of evolution, structure, and the critical mass limit between intermediate and massive stars. We explored the consequences for heavy-element nucleosynthesis during the core carbon-burning phase by means of a one-zone nucleosynthesis code. We confirm the significant impact of using the recent nuclear reaction rates following the fusion suppression hypothesis at deep sub-barrier energies (hindrance hypothesis) as well as the mass-dependent effect of a resonance at 2.14 MeV with dominant feeding of the alpha exit channel of $ C+^ \!C$ fusion reaction. This impacts the characteristics of the core of stars from the C-ignition and during the entire core C-burning phase (temperature and density, lifetime, size, convective or radiative core). The change in nuclear reaction rates modifies the central nucleosynthesis of the stars during the core-carbon burning phase, resulting in an underproduction of s-process elements, especially when including the rotation-induced mixing that amplifies the effects. The correct and accurate determination of the nuclear reaction rates, especially with the existence and location of resonances, impacts stellar evolution in many respects, affecting models' predictions. The choice of the nuclear reaction rates reference for the $ C+^ C$ fusion reaction significantly changes the behaviour of the core during the carbon-burning phase, and consequently drives changes in the nucleosynthesis and end-of-life of stars. This choice needs, then, to be made carefully in order to interpret stellar evolution from the super asymptotic giant branch phase and its massive white dwarf remnants to the core-collapse supernovae of massive stars.
The first stars might have been fast rotators. This would have important consequences for their radiative, mechanical, and chemical feedback. We discuss the impact of fast initial rotation on the evolution of massive Population III models and on their nitrogen and oxygen stellar yields. We explore the evolution of Population III stars with initial masses in the range of 9 msol ini msol starting with an initial rotation on the zero-age main sequence equal to 70<!PCT!> of the critical one. We find that with the physics of rotation considered here, our rapidly rotating Population III stellar models do not follow a homogeneous evolution. They lose very little mass in the case in which mechanical winds are switched on when the surface rotation becomes equal to or larger than the critical velocity. The impact on the ionising flux appears to be modest when compared to moderately rotating models. Fast rotation favours, in models with initial masses above sim 20 msol the appearance of a very extended intermediate convective zone around the H-burning shell during the core He-burning phase. This shell has important consequences for the sizes of the He- and CO-cores, and thus impacts the final fate of stars. Moreover, it has a strong impact on nucleosynthesis, boosting the production of primary 14N. Fast initial rotation significantly impacts the chemical feedback of Population III stars. Observations of extremely metal-poor stars and/or starbursting regions are essential to provide constraints on the properties of the first stars.
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