Ultraviolet Line Profiles of Slowly Rotating Massive Star Winds Using the "Analytic Dynamical Magnetosphere" Formalism

TL;DR

This paper models ultraviolet resonance line profiles in slowly rotating magnetic massive stars using the Analytic Dynamical Magnetosphere formalism, revealing unique redshifted absorption features and the influence of magnetosphere size and line strength.

Contribution

It introduces a combined ADM and radiative transfer approach to systematically study UV line formation in magnetic massive star winds, highlighting the effects of magnetosphere parameters.

Findings

Magnetic massive stars show redshifted absorption in UV lines.

Line profile variations are primarily due to magnetosphere size and wind components.

Cooling parameter has negligible impact on UV line profiles.

Abstract

Recent large-scale spectropolarimetric surveys have established that a small but significant percentage of massive stars host stable, surface dipolar magnetic fields with strengths on the order of kG. These fields channel the dense, radiatively driven stellar wind into circumstellar magnetospheres, whose density and velocity structure can be probed using ultraviolet (UV) spectroscopy of wind-sensitive resonance lines. Coupled with appropriate magnetosphere models, UV spectroscopy provides a valuable way to investigate the wind-field interaction, and can yield quantitative estimates of the wind parameters of magnetic massive stars. We report a systematic investigation of the formation of UV resonance lines in slowly rotating magnetic massive stars with dynamical magnetospheres. We pair the Analytic Dynamical Magnetosphere (ADM) formalism with a simplified radiative transfer technique to produce synthetic UV line profiles. Using a grid of models, we examine the effect of magnetosphere size, the line strength parameter, and the cooling parameter on the structure and modulation of the line profile. We find that magnetic massive stars uniquely exhibit redshifted absorption at most viewing angles and magnetosphere sizes, and that significant changes to the shape and variation of the line profile with varying line strengths can be explained by examining the individual wind components described in the ADM formalism. Finally, we show that the cooling parameter has a negligible effect on the line profiles.