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Paper: B-Type Supergiants in the Magellanic Clouds
Volume: 425, Hot and Cool: Bridging Gaps in Massive Star Evolution
Page: 23
Authors: Lennon, D. J.; Trundle, C.; Hunter, I.; Smartt, S.; Dufton, P.; Evans, C.; Langer, N.; Brott, I.
Abstract: The fact that early B-type supergiants lie in the theoretical blue Hertzsprung gap of the Hertzsprung-Russell Diagram is a long-standing problem in stellar evolution. This has led to considerable uncertainty over the evolutionary status of these stars: Do they indicate a bluewards extension of the hot core-helium-burning phase? If so, then are they pre-Red Supergiant (RSG) or post-RSG stars? Can one broaden the main sequence to partially fill this gap? Does binary evolution provide a significant channel for populating the gap? In this paper we discuss the properties of main-sequence stars and B-type supergiants within the context of the VLT-FLAMES Survey of Massive Stars, which has led to a paradigm shift in our understanding of massive-star evolution. We show that there is now strong evidence from consideration of surface nitrogen abundances in support of the idea that B-type supergiants do {\em not} evolve directly from the main sequence, and that rotational mixing may not be as dominant a process as was previously thought.
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