Resumen
The low excitation events in eta Carinae are known for more than a century, but never fully described. We derived from different features the period P_{pres} = 2022.7+/- 1.3 d, and show that it can't have been changing by more than ΔP/P = 0.0007 over the last 60 years. This gives a strong support to the binary scenario. The so called low excitation event is driven by periastron passage, when the secondary star is deeply immersed in the wind of the primary. We show that the events in the high excitation lines are produced by a blanketing on the radiation field of the secondary star (the ionizing source). We rule out most of the previously proposed mechanisms: such as shell ejection, collapse of the wind-wind collision or eclipse. We show a sample of light curves, exemplifying the peculiarities of each feature, useful for planning monitoring campaigns for the next minimum, predicted to start on 2009/January/11.
