LIGHT VARIATIONS OF MASSIVE STARS (ALPHA-CYGNI VARIABLES) .12. THE PHOTOMETRIC HISTORY OF THE G8IA+ HYPERGIANT V766 CEN (= HR-5171A) DURING THE YEARS 1953-1991 AND ITS INTERPRETATION

VBLUW photometry of the G8 Ia+ hypergiant V 766 Cen (= HR 5171A) made in the interval 1980-1991 is presented and discussed, together with UBV photometry taken from literature, which goes back in time until 1953. The star shows a very strong reddening of approximately 0.m65 between 1953 and 1981, a brightness oscillation with a quasi-period of 494d, in the interval 1973-1991, and a drop in brightness between 1973 and 1977. Whether the strong reddening is caused by an increasing circumstellar dust density or by evolution to the red in the HR diagram is discussed. The radial velocity curve (1979-1981) appears to be in phase with the light curve. This peculiar behaviour is shared with the variable F-type supergiant BL Tel(F). The radius variation amounts to approximately 8%.