Abstract
The evolution of a 20M ⊙ star of extreme Population I (X=0.602,Z=0.044) from the main sequence through the He-exhaustion has been calculated with particular attention to the treatment of the semiconvective zones. Two different relations as convective instability criteria have been adopted ∇ R ⩾∇ a +(β/(4−3β)) (d ln μ/d lnP) or ∇ R ⩾∇ a ). The He-burning phase is substantially different in the two cases. In the first evolutionary picture the star begins the He-burning phase as red supergiant, while in the second one as blue supergiant. The two evolutions are compared with the observational blue to red supergiants ration B/n R in connection with the problem of the existence of the neutrino processes and taking into account the possible presence of a high percentage of binary systems among supergiants.
We draw the conclusion that the massive star evolution seems to be still completely uncertain and also not able to give a decisive test for or against the neutrino emission.
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Chiosi, C., Summa, C. On the evolution of obstars from the main sequence to the Helium exhaustion phase. Astrophys Space Sci 8, 478–496 (1970). https://doi.org/10.1007/BF00651340
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DOI: https://doi.org/10.1007/BF00651340