&theta¹ Ori C is the only O star with a measurable magnetic field, and is also an unusually strong and hard X-ray source. Such behavior is not expected from O stars due to their lack of an outer convective envelope. In this star, radiation-driven wind can, in the presence of the large magnetic field, be channeled along the magnetic field lines. Two streams of wind, one from each hemisphere, will meet at the magnetic equator and collide, creating Magnetically Channeled Wind Shock (MCWS). MCWS leads to higher temperatures than normal wind shock conditions, which leads to the greater production of X-rays.

Previous attempts at simulating such stars have been time-independent and resulted in a post- shock cooling disk, which is found to be unphysical for a variety of reasons. These simulations also did not allow for the distortion of the magnetic field of the star as a result of the wind shock. They did, however, predict the existence of a wind-shock at the magnetic equator. The simulations performed by the authors here expand upon previous simulations to include adiabatic cooling, radiative cooling, and shock heating in the simulation code.

&theta¹ Ori C has an axis of rotation at an angle i = 45 degrees to Earth, and its magnetic axis forms an angle of obliquity &beta = 42 degrees with the rotational axis. As such we can view the star from many angles with respect to its magnetic axis, from nearly edge-on to nearly face-on (rom about 3 to 87 degrees).

The authors used Magneto-hydrodynamic (MHD) simulations designed specifically for this star. For instance, &theta¹ Ori C has a rotational period of about 15 days. As such, the authors decided that any centrifugal or coriolis effects from the rotation would be so small as to be negligable, and hence were ignored during the simulations. The simulations show that the wind shocks create a build-up of matter along the magnetic equator. This build-up is maintained by a balance between gravity, radiative driving, and magnetic tension. During all this, the magnetic field lines of the star are being distorted. At some point, the build-up reaches a critical point and the field lines snap. Some matter is able to escape the star's gravitataional pull, while the rest is subsequently recollected by the star.

These simulations were only performed in 2D, essentially assuming symmetry about the magnetic equator (in other words, it is longitudinally independent). It is found that an X-ray absorbing cooling-disk, as found in earlier simulations, never has a chance to form because of the infall into the photosphere and outflow along the magnetic equitorial plane. In addition, the infalling material is too cool to emit X-rays, and the outflowing material has too low of a density to produce much X-ray emission.

The periodic variability of the X-ray emission from this star, along with the slight increase in column-density when the magnetic equitorial plane is viewed edge-on, imply that the wind-shock region is in fact producing the X-rays. This is because the photosphere regularly occults part (but not all) of the X-ray emitter. As a result, the authors conclude that the MHD simulations and accompanying diagnostics are in excellent agreement with the data collected from Chandra. Also, the new MHD simulations, with adjustments for various parameters discussed earlier, are more accurate that previous simulations which lacked such adjustements.