X-ray and virtual-reality modeling of τ Sco’s magnetosphere

The massive star tau Sco has garnered much observational study due to its intriguing magnetic field structure. Due to its strength, the magnetic field channels the outflowing stellar wind to flow along its magnetic field lines, leading to shocks at the top of closed loops. The resulting hot gas thermally emits in the X-ray band, which has been observed by Chandra, among other X-ray telescopes. Interestingly, the X-ray emission is relatively hard and would not be explained by the typical spatial extent to which tau Sco’s magnetosphere is believed to occupy. However, larger field loops, which allow the wind to accelerate to higher speeds before shocking at the top of the loops, could rectify this issue.

To resolve this discrepancy, as well as to interpret observations in other wavebands, we construct analytic dynamical magnetosphere (ADM) models of tau Sco. Rather than performing computationally expensive MHD simulations, ADM solves analytically for the properties of material flowing along the field lines in three components: the pre-shocked, free-flowing wind, the post-shocked wind still flowing upstream, and the post-shocked wind flowing back towards the stellar surface. These models’ limited computational expense allows a wide range of parameter space to be explored, key among them the mass-loss rate of the star. Furthermore, these ADM models have the necessary ingredients — density and temperature throughout the magnetosphsere — to synthesize the model thermal X-ray emission in order to provide a direct model-to-observation comparison.

This presentation shows several ADM models of tau Sco and their synthesized X-ray emission compared directly to Chandra observations, with the main result being that there is a reduction in tau Sco’s mass-loss rate (to have large enough loops to emit high-energy X-rays), which is consistent with revisions to the properties of other early B-type stars.

For both outreach and research purposes, we will also present “tau Sco VR”, which imports our latest tau Sco ADM models into virtual reality. Through the use of VR goggles and controllers, “tau Sco VR” allows the user to move anywhere they like around the magnetosphere while looking in any direction that they choose. The rendered quantities include open and closed field lines, pre- and post-shocked wind column density, and X-ray emission at various energies across the Chandra band, for example. In addition to discussing how we are adding capabilities to the VR coding to turn the VR into a research tool, we will bring our VR equipment to give live demos to interested parties.