New observations of NGC 1624-2 reveal a complex magnetospheric structure and underlying surface magnetic geometry

TL;DR

This study confirms the complex, dense magnetosphere of NGC 1624-2 and suggests its magnetic field geometry is more intricate than a simple dipole, impacting our understanding of magnetic field origins in massive stars.

Contribution

It provides new observational evidence of a complex magnetospheric structure and non-dipolar magnetic geometry in the most strongly magnetized O-type star.

Findings

NGC 1624-2 hosts a dense, large magnetosphere.

Magnetic field geometry may be more complex than a dipole.

Surface magnetic topology appears to be topologically complex.

Abstract

NGC 1624-2 is the most strongly magnetized O-type star known. Previous spectroscopic observations of this object in the ultraviolet provided evidence that it hosts a large and dense circumstellar magnetosphere. Follow-up observations obtained with the \textit{Hubble Space Telescope} not only confirm that previous inference, but also suggest that NGC 1624-2's magnetosphere has a complex structure. Furthermore, an expanded spectropolarimetric time series shows a potential departure from a dipolar magnetic field geometry, which could mean that the strongest field detected at the surface of an O-type star is also topologically complex. This result raises important questions regarding the origin and evolution of magnetic fields in massive stars.