Two-dimensional simulations of the line-driven instability in hot-star winds

Abstract

We report initial results of two-dimensional simulations of the nonlinear evolution of the line-driven instability (LDI) in hot-star winds. The method is based on the Smooth Source Function (SSF) formalism for nonlocal evaluation of the radial line-force, implemented separately within each of a set of radiatively isolated azimuthal grid zones. The results show that radially compressed "shells" that develop initially from the LDI are systematically broken up by Rayleigh-Taylor or thin-shell instabilities as these structures are accelerated outward. Through radial feedback of backscattered radiation, this leads ultimately to a flow structure characterized by nearly complete lateral incoherence, with structure extending down to the lateral grid scale, which here corresponds to angle sizes of order a fifth of a degree. We briefly discuss the implications for interpreting various observational diagnostics of wind structure, but also emphasize the importance of future extensions to include lateral line-drag effects of diffuse radiation, which may set a minimum lateral scale for break-up of flow structure.