THE OPTICAL AND NEAR-INFRARED VARIABILITY OF ETA-CARINAE - A BINARY LUMINOUS BLUE VARIABLE

We present an analysis of the long-term light variation in the interva l 1935-1992 and of the light and colour variation in VBLUW, uvby and J HKLM photometry in the interval 1971-1992 of eta Carinae. The very lon g-term or secular variation in visual light, showing a smoothed gradua l rise of approximately 1m5 in the interval 1935-1952 and approximatel y 1m in the interval 1952-1992, can be largely attributed to a decreas e of the circumstellar extinction. Evolutionary causes are considered, but seem of negligible importance. An analysis of the light and colou r variations in the interval 1974-1992, revealed the occurrence of at least seven S Dor-type phenomena similar to LBVs on a time scale of 1- 3 yr and amplitudes of 0m1-0m2. Thus the main object is almost certain an LBV. There are also minima of a short duration (a few days?), whic h show a progressively increasing depth to the ultraviolet. A period a nalysis revealed P approximately 52d4, although 104d8 is also possible if secondary minima are present. A few facts cast doubt on the reliab ility of the presumed periodicity, e.g.: the relative large O-C values and the absence of a number of predicted minima. However, these incon sistencies can be explained in terms of an LBV binary, seen at such an inclination angle that the appearance of eclipses depends on the vari able size of the pseudo-photosphere of the LBV primary and on the clum piness of the gaseous material spread around. The variable depth diffe rences between the various pass-bands (sometimes the dips are practica lly undetectable in visual light) suggest atmospheric type of eclipses . The spectral type of the hypothetical small companion, derived from the relative depths in the monochromatic light curves, is early type B V.