Line-drag damping of Alfvén waves in radiatively driven winds of magnetic massive stars

Abstract

Line-driven stellar winds from massive (OB) stars are subject to a strong line-deshadowing instability. Recently, spectropolarimetric surveys have collected ample evidence that a subset of Galactic massive stars hosts strong surface magnetic fields. We investigate here the propagation and stability of magneto-radiative waves in such a magnetised, line-driven wind. Our analytic, linear stability analysis includes line-scattering from the stellar radiation, and accounts for both radial and non-radial perturbations. We establish a bridging law for arbitrary perturbation wavelength after which we analyse separately the long- and short-wavelength limits. While long-wavelength radiative and magnetic waves are found to be completely decoupled, a key result is that short-wavelength, radially propagating Alfvén waves couple to the scattered radiation field and are strongly damped due to the line-drag effect. This damping of magnetic waves in a scattering-line-driven flow could have important effects on regulating the non-linear wind dynamics, and so might also have strong influence on observational diagnostics of the wind structure and clumping of magnetic line-driven winds.

arXiv comment11 pages, 3 figures. Accepted for publication in MNRAS

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Cited by in corpus (3)

• Theoretical wind clumping predictions from 2D LDI models of O-star winds at different metallicities
• Simulations of the line-driven instability in magnetic hot star winds
• Radiation-magnetohydrodynamics with MPI-AMRVAC using flux-limited diffusion