Inclined WWC cavity of η Car and its distorted stellar wind of the primary star. Top: geometric curved shape and orientation of a 3D hydrodynamical simulation of η Car’s WWC cavity (adapted from Fig. 3 in Madura & Groh 2012). The figure shows the LOS view of the geometric shape of the inclined WWC cavity surface, illustrating the orientation of the cavity shape as seen on the sky at orbital phase ϕ = 0.003. The surface of the WWC cavity is color-coded to radius. The dark purple indicates WWC gas at radii of about 75 to 125 au from the primary star. Green indicates gas near the apex of the WWC cavity at a distance of less than 15 au from the primary. The arrows indicate the motion directions of the gas on the cavity surface. The model illustrates that the observer is looking almost parallel along the SE wall of the cavity leading to blue-shifted light emitted from this region. Bottom left: η Car’s aperture-synthesis image at an LOS velocity of − 324 km s⁻¹ with a contour line at 20% of the peak intensity (from Fig. D.1), which illustrates the asymmetry along PA ~120°. The blue-shifted light with an LOS velocity of − 324 km s⁻¹ is more extended to the SE than to the NW, as expected from the orientation of the model of the WWC cavity (top). Bottom right: comparison of the extension of the primary stellar wind (at an LOS velocity of − 8 km s⁻¹; from Fig. 1) with the binary orbit (white) of the secondary star relative to the primary star on the sky. The black dot indicates the position of the primary star. The major axis of the orbit is 30.9 au (Madura et al. 2012; orbit adapted from Teodoro et al. 2016).