2002ApJ...575.1037E

We discuss the evolution of binaries with moderately high masses (∼10-30 M_☉) and with periods of ∼3-300 days, corresponding mostly to early case B. These are usually thought to evolve either by reasonably conservative Roche lobe overflow, if the initial mass ratio is fairly mild, or else by highly nonconservative common-envelope evolution, with spiral-in to short periods (hours, typically), if the initial mass ratio is rather extreme. We discuss here a handful of binaries from part of this period range (∼50-250 days), which appear to have followed a different path: we argue that they must have lost a large proportion of initial mass (∼70%-80%) but without shortening their periods at all. We suggest that their behavior may be due to the fact that stars of such masses, when evolved also to rather large radii, are not far from the Humphreys-Davidson limit, where single stars lose their envelopes spontaneously in P Cygni winds, and so have envelopes that are only lightly bound to the core. These envelopes therefore may be relatively easily dissipated by the perturbing effect of a companion. In addition, some or all of the stars considered here may have been close to the Cepheid instability strip when they filled their Roche lobes. One or the other, or both, of high luminosity and Cepheid instability, in combination with an appropriately close binary companion, may be implicated.