  The periodic spectroscopic events in eta Carinae are now well established and
occur near the periastron passage of two massive stars in a very eccentric
orbit. Several mechanisms have been proposed to explain the variations of
different spectral features, such as an eclipse by the wind-wind collision
boundary, a shell ejection from the primary star or accretion of its wind onto
the secondary. All of them have problems explaining all the observed phenomena.
To better understand the nature of the cyclic events, we performed a dense
monitoring of eta Carinae with 5 Southern telescopes during the 2009 low
excitation event, resulting in a set of data of unprecedented quality and
sampling. The intrinsic luminosity of the He II 4686 emission line (L~310 Lsun)
just before periastron reveals the presence of a very luminous transient source
of extreme UV radiation emitted in the wind-wind collision (WWC) region. Clumps
in the primary's wind probably explain the flare-like behavior of both the
X-ray and He II 4686 light-curves. After a short-lived minimum, He II 4686
emission rises again to a ne
