  Recent spectropolarimetric surveys (MiMeS, BOB) have revealed that
approximately 7% 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 a circumstellar magnetosphere. Wind-sensitive UV
spectral lines can probe the density and velocity structure of massive star
magnetospheres, providing insight into wind-field interactions. To date,
large-scale magnetohydrodynamic modeling of this phenomenon has been limited by
the associated computational cost. Our analysis, using the Analytic Dynamical
Magnetosphere model, solves this problem by applying a simple analytic
prescription to efficiently calculate synthetic UV spectral lines. It can
therefore be applied in the context of a larger parameter study to derive the
wind properties for the population of known magnetic O stars. We also present
the latest UV spectra of the magnetic O star NGC 1624-2 obtained with HST/COS,
which test the limits of our models and suggest a particularly complex
magnetospheric structure for this archetypal object.
