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

• Published in: Monthly notices of the Royal Astronomical Society Vol. 499; no. 3; pp. 4282 - 4292
• Main Authors: Driessen, F A, Kee, N D, Sundqvist, J O, Owocki, S P
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01.12.2020
• Subjects: waves; stars: early-type; stars: magnetic field; stars: winds, outflows; instabilities; radiative transfer
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/staa3196

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 magnetoradiative waves in such a magnetized, 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.