THE 5.52 YEAR CYCLE OF ETA-CARINAE

I have discovered spectroscopic variations correlated with the photome tric near infrared (NIR) light curve in eta Carinae. The fading of the high-excitation lines is coincident with the peaks in the NIR light c urve, strongly resembling an S Doradus type of variability. The cycle, however, is highly stable, and the 5.52 yr period fits well all the s hell episodes reported in the last 50 years. This period also recovers the three historical bursts of the last century, in phase with the pr esent low-amplitude oscillations, which suggests a connection between the S Doradus cycle and the giant bursts. The present data reveal that eta Car is continuously varying in the He I lambda 10830 line by thou sands of solar luminosities. The last spectra in this line show that t he low-excitation phase is already in progress. A test for the strict periodicity will be the confirmation of the central phase epoch of the next shell event, predicted to occur in 1997 December. A very sensiti ve mapping technique is also proposed for this occasion, in order to p rove Homunculus geometry.