Diffusion-plus-drift models for the mass leakage from centrifugal magnetospheres of magnetic hot-stars

TL;DR

This paper develops a semi-analytic model for the mass distribution and emission diagnostics of centrifugally supported magnetospheres in magnetic hot stars, incorporating diffusion and drift processes.

Contribution

It introduces a novel diffusion-plus-drift framework to analyze mass leakage in stellar magnetospheres, providing scaling relations for observational diagnostics.

Findings

Derived equilibrium mass distribution scaling relations.

Estimated diffusion and drift coefficients for turbulent magnetic fields.

Applied model to interpret emission line surveys of OB stars.

Abstract

In the subset of luminous, early-type stars with strong, large-scale magnetic fields and moderate to rapid rotation, material from the star's radiatively driven stellar wind outflow becomes trapped by closed magnetic loops, forming a centrifugally supported, co-rotating magnetosphere. We present here a semi-analytic analysis of how this quasi-steady accumulation of wind mass can be balanced by losses associated with a combination of an outward, centrifugally driven drift in the region beyond the Kepler co-rotation radius, and an inward/outward diffusion near this radius. We thereby derive scaling relations for the equilibrium spatial distribution of mass, and the associated emission measure for observational diagnostics like Balmer line emission. We discuss the potential application of these relations for interpreting surveys of the emission line diagnostics for OB stars with centrifugally supported magnetospheres. For a specific model of turbulent field-line-wandering rooted in surface motions associated with the iron opacity bump, we estimate values for the associated diffusion and drift coefficients.