Luminous Blue Variables & Mass Loss near the Eddington Limit

TL;DR

This paper reviews the mechanisms of mass loss in massive stars, focusing on line-driven winds and continuum driving during LBV eruptions near the Eddington limit, highlighting the role of porosity and flow dynamics.

Contribution

It introduces a detailed analysis of continuum driving and porosity effects in LBV mass loss, contrasting with traditional line-driven wind models.

Findings

Continuum driving can reach the photon-tiring limit, explaining large mass loss in LBV eruptions.

Porosity in stellar atmospheres regulates continuum-driven mass loss.

Time-dependent simulations show complex inflow and outflow dynamics near the tiring limit.

Abstract

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.