Search for: All records

Abstract The radioisotope 26 Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26 Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch stars; to massive and very massive stars, both their Wolf–Rayet winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several reactions affect the production of 26 Al in these astrophysical objects, including (but not limited to) 25 Mg( p , γ ) 26 Al, 26 Al( p , γ ) 27 Si, and 26 Al( n , p / α ). Extensive experimental effort has been spent during recent years to improve our understanding of such key reactions. Here we present a summary of the astrophysical motivation for the study of 26 Al, a review of its production in the different stellar sites, and a timely evaluation of the currently available nuclear data. We also provide recommendations for the nuclear input into stellar models and suggest relevant, future experimental work. 

ABSTRACT Evolved Wolf–Rayet stars form a key aspect of massive star evolution, and their strong outflows determine their final fates. In this study, we calculate grids of stellar models for a wide range of initial masses at five metallicities (ranging from solar down to just 2 per cent solar). We compare a recent hydrodynamically consistent wind prescription with two earlier frequently used wind recipes in stellar evolution and population synthesis modelling, and we present the ranges of maximum final masses at core He-exhaustion for each wind prescription and metallicity Z. Our model grids reveal qualitative differences in mass-loss behaviour of the wind prescriptions in terms of ‘convergence’. Using the prescription from Nugis & Lamers the maximum stellar black hole is found to converge to a value of 20–30 M⊙, independent of host metallicity; however, when utilizing the new physically motivated prescription from Sander & Vink there is no convergence to a maximum black hole mass value. The final mass is simply larger for larger initial He-star mass, which implies that the upper black hole limit for He-stars below the pair-instability gap is set by prior evolution with mass loss, or the pair instability itself. Quantitatively, we find the critical Z for pair-instability (ZPI) to be as high as 50 per cent Z⊙, corresponding to the host metallicity of the Large Magellanic Cloud. Moreover, while the Nugis & Lamers prescription would not predict any black holes above the approx 130 M⊙ pair-instability limit, with Sander & Vink winds included, we demonstrate a potential channel for very massive helium stars to form such massive black holes at ∼2 per cent Z⊙ or below.