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Paper: Chemical Abundances and Yields from Massive Stars
Volume: 336, COSMIC ABUNDANCES as Records of Stellar Evolution and Nucleosynthesis in honor of David L. Lambert
Page: 79
Authors: Maeder, A.; Meynet, G.; Hirschi, R.
Abstract: Stellar rotation produces an internal mixing of the elements due to shear instability and meridional circulation. This leads to observable N/C enhancements in massive stars above about 7-9 MSolar. Rotation also favors mass loss by stellar winds. Mass loss effects dominate for masses above 30 MSolar, while mixing dominates below that limit. The effects of mixing are also much larger at lower metallicity Z, because the internal Ω-gradients are steeper. This appears to be in agreement with observations in the SMC.

At very low Z and Z = 0, mixing between the He-burning core and the H-burning shell leads to the production of primary N in intermediate mass stars. Such enrichments increase the metallicity of the rotating star, also massive Z = 0 stars with moderate initial velocities currently reach break-up velocity during a fraction of the MS phase. Both effects favor mass loss in Z = 0 stars, which have ejecta with abundance anomalies very similar to those of C-rich very metal poor stars.

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