Multiperiodic variations in the last 104-yr light curve of the symbiotic star BF Cyg

ABSTRACT We analyse a light curve (LC) of the symbiotic star BF Cyg, covering 114 yr 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....

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2006-02, Vol.366 (2), p.675-681
Main Authors: Leibowitz, E. M., Formiggini, L.
Format: Article
Language:English
Subjects:
Astronomy
binaries: symbiotic
Earth, ocean, space
Exact sciences and technology
Magnetic fields
Orbits
Starbursts
Stars & galaxies
stars: individual: BF Cyg
stars: magnetic fields
stars: oscillations
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Summary:ABSTRACT We analyse a light curve (LC) of the symbiotic star BF Cyg, covering 114 yr 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 six less intense outbursts of 1–2 mag and duration of 2000–5000 d. We find a cycle of 6376 d, 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‐d magnetic cycle of our Sun. We further find, that in addition to its well‐known binary period of 757.3 d, BF Cyg possesses also another photometric period of 798.8 d. This could be the rotation period of the giant star of the system. If it is, the beat period of these two periodicities, 14 580 d, is the rotation period of a tidal wave on the surface of the giant. A fourth period of 4436 d, the beat period of the 14 580‐d and the 6376‐d 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‐d period explains the disappearance of the orbital modulation at some epochs in the LC. The 757.3‐d oscillations will be damped again around the year 2013.
ISSN:0035-8711
1365-2966
DOI:10.1111/j.1365-2966.2005.09895.x