Simulations of the line-driven instability in magnetic hot star winds

TL;DR

This study uses 2D MHD simulations to explore how magnetic fields influence the line-driven instability in hot star winds, revealing large-scale shell structures that differ from non-magnetic clumping.

Contribution

First direct investigation of LDI effects in magnetic hot star winds using 2D MHD simulations, highlighting the impact of magnetic confinement on wind morphology.

Findings

Magnetic confinement alters wind structure from small clumps to large-scale shells.

LDI leads to shellular sheets in magnetic winds, unlike in non-magnetic winds.

Results have implications for observational diagnostics and stellar evolution models.

Abstract

Line-driven winds of hot, luminous stars are intrinsically unstable due to the line-deshadowing instability (LDI). In non-magnetic hot stars, the LDI leads to the formation of an inhomogeneous wind consisting of small-scale, spatially separated clumps that can have great effects on observational diagnostics. However, for magnetic hot stars the LDI generated structures, wind dynamics, and effects on observational diagnostics have not been directly investigated so far. We investigated the non-linear development of LDI generated structures and dynamics in a magnetic line-driven wind of a typical O-supergiant. We employed two-dimensional axisymmetric magnetohydrodynamic (MHD) simulations of the LDI using the Smooth Source Function approximation for evaluating the assumed one-dimensional line force. To facilitate the interpretation of these magnetic models, they were compared with a corresponding non-magnetic LDI simulation as well as a magnetic simulation neglecting the LDI. A central result obtained is that the wind morphology and wind clumping properties change strongly with increasing wind-magnetic confinement. Most notably, in magnetically confined flows, the LDI leads to large-scale, shellular sheets ('pancakes') that are quite distinct from the spatially separate, small-scale clumps in non-magnetic line-driven winds. We discuss the impact of these findings for observational diagnostic studies and stellar evolution models of magnetic hot stars.