Quote:the mass-donor star ---the one that eventually explodes---
Scopes: CPC8, TV85+Voyager Binos: 40-70mm, GT80mm~45deg
"We live in the sky, not under it." John Tyndall
Quote:They don't talk very much about why the star was yellow when it blew up in the paper (I didn't see any significant discussion of it at all when I skimmed it, actually). They give most of their time to arguing that it was a binary, and that the progenitor was an extended object (i.e., a star with nuclear burning in the core as opposed to a degenerate remnant).If I had to guess why the star was yellow, it's that the companion was siphoning off enough mass for the star to be much smaller than it would have been were it a single star. Since the energy generation in the core would be basically fixed no matter what the extended part of the envelope is doing, as the star gets smaller, the surface gets hotter and bluer. If the star had been alone, it would have exploded as a red supergiant.
Quote:Massive stars need not necessarily be in the *red* supergiant phase at the moment of core collapse. Such stars--if of sufficient mass--are believed to re-cross the Cepheid instability strip a couple or more times. The core could conceivably collapse at most any stage of this process.The presence of the companion may have little impact, at least as far as its 'robbing' of some of the outer envelope of the other star is concerned. The veritable vaccuum of the tenuous envelope has nothing, really, to do with what's going on in the comparatively minute (planet-sized), super-dense core.