Testing Radiative Braking with XMM and NuSTAR observations of the closest Colliding Wind Binary γ2 Velorum

We obtained multiple epochs of XMM observations of γ2 Velorum in late 2016, as well as joint XMM/NuSTAR observations in late 2018. These new x-ray observations are compared to smoothed-particle hydrodynamical models for the system based on the visual and spectroscopic orbit and the inferred mass-loss rates for the component stars. Our models are able to qualitatively describe spectroscopic variability in the optical, including absorption profiles in neutral helium and emission excess in C III. However, these models are not yet able to reproduce the X-ray fluxes and the variable absorption as the shock cone moves in and out of our line of sight. We think the modeling problems with the x-ray emission are due to radiative braking not being taken into effect yet, and we describe new modeling efforts to better understand this key system to our understanding of colliding winds.