Simulating the Interaction between Radiation Driven Stellar Wind and Magnetic Field Using Riemann Geomesh MHD Code

Massive O and B stars emit around 50% of their initial mass via stellar winds throughout their lifespan. Simulating and analyzing winds from magnetic massive stars aids in comprehending their evolution and nearby interstellar gas cloud turbulence. However, simulating magnetic massive stars remains challenging due to limitations in the simulation tools that were employed. The recent Riemann Geomesh MHD code can handle high rotation rates and large magnetic tilt angles, thereby facilitating a comprehensive analysis of stellar winds and the X-ray emission from magnetic massive stars.

Given this, the present work utilizes the state-of-the-art MHD algorithms of the Riemann Geomesh code. The first set of simulations adopts an isothermal MHD approach to investigate the overall dynamics of magnetically channeled winds at varying magnetic tilt angles and high rotation rates. The simulations are run up to a quasi-steady state, revealing the episodic centrifugal breakout events of the mass outflow, confined by the magnetic field loops that form the closed magnetosphere of the star. The catalogued results provide perspective on how angular momentum varies for different configurations of rotation rate, magnetic field strength, and large magnetic tilt angles.

The second set of simulations is performed to study the high-temperature X-ray emission from θ1 Orionis C. The simulations incorporate the energy equation and cooling terms to model the formation and cooling of dense shock regions. The simulated data consistently reproduces the peaks and interesting positive slope in the X-ray emission measure distribution of θ1 Orionis C, as obtained from the Chandra data. Additionally, the total X-ray luminosity from the simulated data aligns well within the observed range of θ1 Orionis C. As part of this work, a vectorized, cube-sphere version of the Riemann Geomesh code is accelerated using GPUs, resulting in 5 times faster performance on GPUs.