3D MHD models of the centrifugal magnetosphere from a massive star with an oblique dipole field

TL;DR

This paper presents 3D MHD simulations of the magnetospheres of massive stars with oblique dipole magnetic fields, revealing how magnetic and rotational axes influence the structure and density distribution of the star's centrifugal magnetosphere.

Contribution

It introduces self-consistent 3D MHD models of oblique stellar magnetospheres, extending previous analytic models to include magnetic warping and density structures.

Findings

Accumulation surfaces resemble RRM model predictions.

Magnetic field distortion occurs near critical mass buildup.

Density concentrates in wings near magnetic and rotational equators.

Abstract

We present results from new self-consistent 3D MHD simulations of the magnetospheres from massive stars with a dipole magnetic axis that has a non-zero obliquity angle ($\beta$) to the star's rotation axis. As an initial direct application, we compare the global structure of co-rotating disks for nearly aligned ($\beta=5^o$) versus half-oblique ($\beta=45^o$) models, both with moderately rapid rotation ($\sim$ 0.5 critical). We find that accumulation surfaces broadly resemble the forms predicted by the analytic Rigidly Rotating Magnetosphere (RRM) model, but the mass buildup to near the critical level for centrifugal breakout against magnetic confinement distorts the field from the imposed initial dipole. This leads to an associated warping of the accumulation surface toward the rotational equator, with the highest density concentrated in {\em wings} centered on the intersection between the magnetic and rotational equators. These MHD models can be used to synthesize rotational modulation of photometric absorption and H$\alpha$ emission for a direct comparison with observations.