Modelling the radio light curve of η Carinae

We study the propagation of the ionizing radiation emitted by the secondary star in η Carinae. We find that a large fraction of this radiation is absorbed by the primary stellar wind, mainly after it encounters the secondary wind and passes through a shock wave. The amount of absorption depends on the compression factor of the primary wind in the shock wave. We build a model where the compression factor is limited by the magnetic pressure in the primary wind. We find that the variation of the absorption by the post-shock primary wind with orbital phase changes the ionization structure of the circumbinary gas and can account for the radio light curve of η Car. Fast variations near periastron passage are attributed to the onset of the accretion phase.