New Insights into the Puzzling P-Cygni Profiles of Magnetic Massive Stars

Magnetic massive stars comprise approximately 10% of the total OB star population. Modern spectropolarimetry shows these stars host strong, stable, large-scale, often nearly dipolar surface magnetic fields of 1 kG or more. These global magnetic fields trap and deflect outflowing stellar wind material, forming an anisotropic magnetosphere that can be probed with wind-sensitive UV resonance lines. Recent HST UV spectra of NGC 1624-2, the most magnetic O star observed to date, show atypically unsaturated P-Cygni profiles in the Civ resonant doublet, as well as a distinct variation with rotational phase. We examine the effect of non-radial, magnetically-channeled wind outflow on P-Cygni line formation, using a Sobolev Exact Integration (SEI) approach for direct comparison with HST UV spectra of NGC 1624-2. We demonstrate that the addition of a magnetic field desaturates the absorption trough of the P-Cygni profiles, but further efforts are needed to fully account for the observed line profile variation. Our study thus provides a first step toward a broader understanding of how strong magnetic fields affect mass loss diagnostics from UV lines.

Growth of the line-profile variation region during Be episodes

We have found that the range in wavelength of the line-profile variations (lpv) in the Be star λ Eridani increases by some 20% during its emission phases. This growth is associated with a possible increase in the equatorial velocity of the star during emission. We discuss the significance of this in connection with other features of the lpv and our earlier discovery of a weak correlation between the amplitude of the lpv and Be outbursts in ζ Ophiuchi.