A PULSATING STAR INSIDE ETA-CARINAE .1. LIGHT VARIATIONS, 1992-1994

We present and analyze two seasons of intense photometric monitoring i n the Stromgren uvbyH beta system of eta Carinae (October 1992-August 1994). The luminous blue variable (LBV) in the core did not show much S Dor activity, i.e. it was in a relatively quiescent stage. This situ ation was very favourable for studying its optical micro variations. I t appears that the cen tral LBV pulsates (presumably in a non-radial m ode) like other massive evolved stars, the alpha Cyg variables. The qu asi-period is 58(d)56. The linear ephemeris is: JD(max) = 2448875.0 58.56E. Support was found for the existence of the presumed periodicit y of 52(d)4 of the so-called ''dimples'', shallow dips in the light cu rve which only last for a few days. The cause may be the eclipse of a small companion or of a hot spot in an accretion disk. The H beta inde x became bluer by similar to 0(m)07 during the last 1 1/2 years and sh ows an oscillation in anti-phase with the 58(d)56 pulsation, suggestin g that the HII region(s) responsible for the hydrogen line emission ha s a relatively high luminosity. This is another reason to suppose that a second luminous source, perhaps a luminous disk (with a hot spot), may be present in the eta Car system.