Eta Carinae at radio wavelengths

Eta Carinae is one of the most luminous stars in our Galaxy; It suffered a giant eruption in the 19th century when ejected a 
bipolar Nebula, the Homunculus. Currently the star is hidden by a cloud of gas and dust, preventing its direct observation. The 
existence of a periodicity of 2022 days in the light curve of the high excitation lines, as well as in the radial velocity of H 
recombinant lines, can be very well explained by a binary system with high eccentricity. The observed high X-ray emission 
results naturally from the collision between the stellar winds in the binary system. The geometric and physical parameters of 
the shock region vary quickly as the stars approach each other. The gas cools and accumulates in the orbital plane, forming 
a disk, which is observed in radio waves. The flux density increases with frequency, as expected of thermal radiation from 
optically thick plasma. The emission varies periodically during the cycle, in phase with the light curves in optical and X-rays. 
We will present the light curves of the last two orbital periods, obtained at 7 mm (43 GHz) with the Itapetinga radiotelescope, 
showing that the flux density is more than 50 percent higher during this last cycle, in contrast with the X-rays, which present 
a decrease. Recombination lines of  H and He are also observed at radio wavelengths, showing strong maser emission. We 
will present observations of the H40, H35, H30 and H26 alpha lines, observed with SEST and APEX.