On the Role of Continuum-driven Eruptions in the Evolution of Very Massive Stars and Population III Stars

We suggest that the mass lost during the evolution of very massive stars maybe dominated by optically thick, continuum-driven outbursts or explosions,instead of by steady line-driven winds. In order for a massive star to become aWR star, it must shed its H envelope, but new estimates of the effects ofclumping in winds indicate that line driving is vastly insufficient. We discussmassive stars above roughly 40-50 Msun, for which the best alternative is massloss during brief eruptions of luminous blue variables (LBVs). Our clearestexample of this phenomenon is the 19th century outburst of eta Car, when thestar shed 12-20 Msun or more in less than a decade. Other examples arecircumstellar nebulae of LBVs, extragalactic eta Car analogs (``supernovaimpostors''), and massive shells around SNe and GRBs. We do not yet fullyunderstand what triggers LBV outbursts, but they occur nonetheless, and presenta fundamental mystery in stellar astrophysics. Since line opacity from metalsbecomes too saturated, the extreme mass loss probably arises from acontinuum-driven wind or a hydrodynamic explosion, both of which areinsensitive to metallicity. As such, eruptive mass loss could have played apivotal role in the evolution and fate of massive metal-poor stars in the earlyuniverse. If they occur in these Population III stars, such eruptions wouldprofoundly affect the chemical yield and types of remnants from early SNe andhypernovae.Comment: 4 pages, 1 figure, accepted by ApJ Letter