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You've pretty much hit the nail on the head there, Les, except that the most massive of stars don't go through the WR stage either. There seems to be a cutoff at around 70 solar masses where stars can't expel enough mass via stellar wind to become WR stars. The progenitors of WR stars weigh in between 40-70 solar masses and usually form from stars around 50-60 solar masses...at least it appears these stars are the most likely to become WR stars. Smaller stars around the 40 solar mass mark can either go WR or become red supergiants, depending on the initial conditions within the stars as they leave the main sequence...it's all dependent on mass loss rates during the giant/supergiant phases of the star's evolution. The largest of stars (LBV's...hypergiants)...the eta Carina's, Pistol Star's and the ilk....tend to go off as hypernovae and create short period GRB's.
As you've said, red supergiants aren't always necessarily the most massive or brightest of stars. They usually form from stars between 10-40 solar masses as these stars can maintain hydrostatic equilibrium as red supergiants.
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