High-energy Transmission Grating Spectroscopy and 3D Wind Shock Simulations of the Magnetic Massive Star θ¹ Orionis C

The Chandra X-ray Observatory has completed a 2.1-Ms Very Large Program to observe the Trapezium Cluster with the High-Energy Transmission Grating Spectrometer. The brightest source is the magnetic O7 Vp star θ¹ Ori C, the central star of the Orion Nebula. We present a spectroscopic analysis of the 1.5–20 Å spectrum, including a detailed analysis of the forbidden, intercombination and resonance lines of He-like ions of Ar XVII, S XV, Si XIII, and Mg XI. In particular, we explicitly account for emission from weak lines, including dielectronic recombination lines, in our analysis of the He-like line complexes. An ISIS fit of the entire spectrum is used to estimate the emission-measure distribution of the shock plasma, while the He-like f/i ratios are used to constrain the approximate location of the shocks. Emission-line profiles are analyzed to measure Doppler velocities. We also present 3D magnetohydrodynamic shock simulations of the magnetized wind of θ¹ Ori C using the newly developed Riemann Geomesh code, which uses an isotropic triangular geodesic mesh to map the spherical surface of the star, and a non-linear radial zone structure to map the volume of the wind. From the simulations we generate synthetic emission-measure distributions, column densities, Doppler widths, X-ray luminosities and radial shock distributions, for direct comparison with observational diagnostics.