## On the role of continuum-driven eruptions in the evolution of very massive stars and Population III stars

Nathan Smith (1) and Stanley P. Owocki (2)

(1) U. Colorado, and (2) U. Delaware

We suggest that the mass lost during the evolution of very massive
stars may be dominated by optically thick, continuum-driven outbursts
or explosions, instead of by steady line-driven winds. In order for a
massive star to become a Wolf-Rayet star, it must shed its hydrogen
envelope, but new estimates of the effects of clumping in winds from
O-type stars indicate that line driving is vastly insufficient. We
discuss massive stars above roughly 40--50 M$_{\odot}$, which do not
become red supergiants, and for which the best alternative is mass
loss during brief eruptions of luminous blue variables (LBVs). Our
clearest example of this phenomenon is the 19th century outburst of
$\eta$ Carinae, when the star shed 12--20 M$_{\odot}$ or more in less
than a decade. Other examples are circumstellar nebulae of LBVs and
LBV candidates, extragalactic $\eta$ Car analogs (the so-called
supernova impostors''), and massive shells around supernovae and
gamma-ray bursters. We do not yet fully understand what triggers LBV
outbursts or what supplies their energy, but they occur nonetheless,
and present a fundamental mystery in stellar astrophysics. Since line
opacity from metals becomes too saturated, the extreme mass loss
probably arises from a continuum-driven wind or a hydrodynamic
explosion, both of which are insensitive to metallicity. As such,
eruptive mass loss could have played a pivotal role in the evolution
and ultimate fate of massive metal-poor stars in the early universe.
If they occur in these Population III stars, such eruptions would also
profoundly affect the chemical yield and types of remnants from early
supernovae and hypernovae thought to be the origin of long gamma ray
bursts.

Reference: 2006, ApJ, 645, L45
Status: Manuscript has been accepted