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| Paper: |
Tepid Supergiants: Chemical Signatures of Stellar Evolution and the Extent of Blue Loops |
| Volume: |
425, Hot and Cool: Bridging Gaps in Massive Star Evolution |
| Page: |
134 |
| Authors: |
Przybilla, N.; Firnstein, M.; Nieva, M.-F. |
| Abstract: |
Massive stars can develop into tepid supergiants at several stages of their post main-sequence evolution, prior to core He-burning, on a blue loop, or close to the final supernova explosion. We discuss observational constraints on models of massive star evolution obtained from the analysis of a sample of Galactic supergiants and put them in the context of the cosmic abundance standard, as recently proposed from the study of their OB-type progenitors (Z = 0.014 for stars in the solar neighborhood). High-precision abundance analyses for He and CNO, with uncertainties as low as ∼10–20%, trace the transport efficiency of nuclear-processed material to the stellar surface, either by rotational mixing or during the first dredge-up. A mixing efficiency that is a factor of ∼2 higher than predicted by current evolution models for rotating stars is implied, suggesting that additional effects, e.g., the interplay of circulation and magnetic fields, need to be considered in evolutionary models. Blue loops probably extend to higher masses and higher effective temperatures than predicted by the current generation of stellar evolution models. |
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