Super-Eddington stellar winds driven by near-surface energy deposition

Abstract

We develop analytic and numerical models of the properties of super-Eddington stellar winds, motivated by phases in stellar evolution when super-Eddington energy deposition (via, e.g. unstable fusion, wave heating, or a binary companion) heats a region near the stellar surface. This appears to occur in the giant eruptions of luminous blue variables (LBVs), Type IIn supernovae progenitors, classical novae, and X-ray bursts. We show that when the wind kinetic power exceeds Eddington, the photons are trapped and behave like a fluid. Convection does not play a significant role in the wind energy transport. The wind properties depend on the ratio of a characteristic speed in the problem vcrit ~ (E˙G)1/5 (where E˙ is the heating rate) to the stellar escape speed near the heating region vesc(rh). For vcrit ≥ vesc(rh), the wind kinetic power at large radii E˙w ~ E˙. For vcrit ≤ vesc(rh), most of the energy is used to unbind the wind material and thus E˙w ≤ E˙. Multidimensional hydrodynamic simulations without radiation diffusion using flash and one-dimensional hydrodynamic simulations with radiation diffusion using mesa are in good agreement with the analytic predictions. The photon luminosity from the wind is itself super-Eddington but in many cases the photon luminosity is likely dominated by 'internal shocks' in the wind. We discuss the application of our models to eruptive mass-loss from massive stars and argue that the wind models described here can account for the broad properties of LBV outflows and the enhanced mass-loss in the years prior to Type IIn core-collapse supernovae.