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The evolution of a 20 Mₛun_ star with a metallicity appropriate for the Large Magellanic Cloud (Z = 0. 005 for most calculations) is investigated in order to determine under which assumptions the star will finally resemble the progenitor star of SN 1987A (Sk -69ᵈeg²02), i. e. , having an effective temperature of ~ 15, 000 K. Low metallicities and restricted mixing in the semiconvective layers are favoring a final evolution as a blue supergiant, while (moderate) mass loss and high carbon abundances after helium burning are doing the opposite. Combining low metallicity, restricted semiconvective mixing, and moderate mass loss results in a blue progenitor. The uncertainties of the results due to the sensitive dependence of the evolution on the assumptions are stressed. The results are also compared with previous, independent calculations. The connection with observed red-to-blue ratios is also shortly discussed.
Achim Weiß (Sat,) studied this question.