The departure of η Carinae from axisymmetry and the binary hypothesis

I argue that the large‐scale departure from axisymmetry of the η Carinae nebula can be explained by the binary star model of η Carinae. The companion diverts the wind blown by the primary star, by accreting from the wind and possibly by blowing its own collimated fast wind (CFW). The effect of these processes depends on the orbital separation, and hence on the orbital phase of the eccentric orbit. The variation of the mass outflow from the binary system with the orbital phase leads to a large‐scale departure from axisymmetry along the equatorial plane, as is observed in η Carinae. I further speculate that such a companion may have accreted a large fraction of the mass that was expelled in the Great Eruption of 1850 and the Lesser Eruption of 1890. The accretion process was likely to form an accretion disc, with the formation of a CFW, or jets, on the two sides of the accretion disc. The CFW may have played a crucial role in the formation of the two lobes.