Luminous Blue Variables & Mass Loss near the Eddington Limit

Stanley P. Owocki$^1$,
Allard Jan van Marle$^1$

1-Bartol Research Institute, Department of Physics & Astronomy, University of Delaware

During the course of their evolution, massive stars lose a substantial
fraction of their initial mass, both through steady winds and through
relatively brief eruptions during their Luminous Blue Variable (LBV)
phase. This talk reviews the dynamical driving of this mass loss,
contrasting the line-driving of steady winds to the potential role of
continuum driving for eruptions during LBV episodes when the star
exceeds the Eddington limit. A key theme is to emphasize the inherent
limits that self-shadowing places on line-driven mass loss rates,
whereas continuum driving can in principle drive mass up to the
``photon-tiring" limit, for which the energy to lift the wind becomes
equal to the stellar luminosity. We review how the ``porosity" of a
highly clumped atmosphere can regulate continuum-driven mass loss,
but also discuss recent time-dependent simulations of how base mass flux
that exceeds the tiring limit can lead to flow stagnation and a complex,
time-dependent combination of inflow and outflow regions.
A general result is thus that porosity-mediated continuum driving in
super-Eddington phases can explain the large, near tiring-limit mass loss
inferred for LBV giant eruptions.

Reference: Invited review, Massive Stars as Cosmic Engines, IAU Symp 250, ed. F. Bresolin, P. A. Crowther, & J. Puls (Cambridge Univ. Press)
Status: Conference proceedings