Multi-periodic variations in the last 104 years light curve of the   symbiotic star BF Cyg
  We analyse a light curve of the symbiotic star BF Cyg, covering 114 years of its photometric history. The star had a major outburst around the year 1894. Since then the mean optical brightness of the system is in steady decline, reaching only in the last few years its pre-outburst value. Superposed on this general decline are some 6 less intense outbursts of 1-2 magnitude and duration of 2000-5000 days. We find a cycle of ~6376 days, or possibly twice this period, in the occurrence of these outbursts. We suggest that the origin of the system outbursts is in some magnetic cycle in the outer layers of the giant star of the system, akin to the less intense ~8000 days magnetic cycle of our Sun. We further find, that in addition to its well known binary period of 757.3 days, BF Cyg possesses also another photometric period of 798.8 days. This could be the rotation period of the giant star of the system. If it is, the beat period of these two periodicities, 14580 days, is the rotation period of a tidal wave on the surface of the giant. A 4th period of 4436 days, the beat period of the 14580 and the 6376 cycles is possibly also present in the LC. We predict that BF Cyg will be at the peak of its next outburst around the month of May in the year 2007. The newly discovered 798.8 days period explains the disappearance of the orbital modulation at some epochs in the light curve. The 757.3 oscillations will be damped again around the year 2013. 
Elia Leibowitz and Liliana Formiggini (Tel Aviv University-Israel)