3 PERIODICITIES IN A 98-YEAR LIGHT-CURVE OF THE SYMBIOTIC STAR Z-ANDROMEDAE

Combining data from various sources we present a visual light curve of the symbiotic star Z Andromedae, covering continuously 98 years of th is star's photometric history. Tune series analysis reveals a clear, c oherent periodicity of 759 days in the light curve, with epoch of mini mum light at JD 2442666. We identify this period as the binary period of the star. During outbursts, the star enters an oscillation mode wit h a quasi-period of 656 days. These oscillations may include a stable, coherent component with a period of 667 days. A third periodicity of similar to 5500 days is also present in the data. It is the beat perio d between the binary and the high state cycles of Z And. It is found i n the light curve of the low state of the star. The light variability of Z And during two, and possibly also a third, major outbursts, out o f the 5 observed in the last 98 years, may be fitted to a model of dam ped driven oscillator.