Activity cycle of the giant star of Z Andromedae and its spin period
We have re-analysed the long-term optical light curve (LC) of the symbiotic star Z Andromedae, covering 112 yr of mostly visual observations. Two strictly periodic cycles and one quasi-periodic cycle can be identified in this LC. A P 1 = 7550 d quasi-periodicity characterizes the repetition time of...
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fthighwire:oai:open-archive.highwire.org:mnras:385/1/445 2023-05-15T17:40:03+02:00 Activity cycle of the giant star of Z Andromedae and its spin period Leibowitz, Elia M. Formiggini, Liliana 2008-03-21 00:00:00.0 text/html http://mnras.oxfordjournals.org/cgi/content/short/385/1/445 https://doi.org/10.1111/j.1365-2966.2008.12847.x en eng Oxford University Press http://mnras.oxfordjournals.org/cgi/content/short/385/1/445 http://dx.doi.org/10.1111/j.1365-2966.2008.12847.x Copyright (C) 2008, Oxford University Press Papers TEXT 2008 fthighwire https://doi.org/10.1111/j.1365-2966.2008.12847.x 2013-05-27T04:13:59Z We have re-analysed the long-term optical light curve (LC) of the symbiotic star Z Andromedae, covering 112 yr of mostly visual observations. Two strictly periodic cycles and one quasi-periodic cycle can be identified in this LC. A P 1 = 7550 d quasi-periodicity characterizes the repetition time of the outburst episodes of this symbiotic star. Six such events have been recorded so far. During quiescence states of the system, that is, in time-intervals between outbursts, the LC is clearly modulated by a stable coherent period of P 2 = 759.1 d. This is the well-known orbital period of the Z Andromedae binary system that has been measured also spectroscopically. A third coherent period of P 3 = 658.4 d is modulating the intense fluctuations in the optical brightness of the system during outbursts. We attribute the trigger of the outburst phenomenon and the clock that drives it, to a solar-type magnetic dynamo cycle that operates in the convection and the outer layers of the giant star of the system. We suggest that the intense surface activity of the giant star during maximum phases of its magnetic cycle is especially enhanced in one or two antipode regions, fixed in the atmosphere of the star and rotating with it. Such spots could be active regions around the North Pole and the South Pole of a general magnetic dipole field of the star. The P3 periodicity is half the beat of the binary orbital period of the system and the spin period of the giant. The latter is then either 482 or 1790 d. If only one pole is active on the surface of the giant, P3 is the beat period itself, and the spin period is 352 d. It could also be 5000 d if the giant is rotating in a retrograde direction. We briefly compare these findings in the LC of Z Andromedae to similar modulations that were identified in the LC of two other prototype symbiotics, BF Cyg and YY Her. Text North Pole South pole HighWire Press (Stanford University) South Pole North Pole Monthly Notices of the Royal Astronomical Society 385 1 445 452 |
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Papers Leibowitz, Elia M. Formiggini, Liliana Activity cycle of the giant star of Z Andromedae and its spin period |
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Papers |
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We have re-analysed the long-term optical light curve (LC) of the symbiotic star Z Andromedae, covering 112 yr of mostly visual observations. Two strictly periodic cycles and one quasi-periodic cycle can be identified in this LC. A P 1 = 7550 d quasi-periodicity characterizes the repetition time of the outburst episodes of this symbiotic star. Six such events have been recorded so far. During quiescence states of the system, that is, in time-intervals between outbursts, the LC is clearly modulated by a stable coherent period of P 2 = 759.1 d. This is the well-known orbital period of the Z Andromedae binary system that has been measured also spectroscopically. A third coherent period of P 3 = 658.4 d is modulating the intense fluctuations in the optical brightness of the system during outbursts. We attribute the trigger of the outburst phenomenon and the clock that drives it, to a solar-type magnetic dynamo cycle that operates in the convection and the outer layers of the giant star of the system. We suggest that the intense surface activity of the giant star during maximum phases of its magnetic cycle is especially enhanced in one or two antipode regions, fixed in the atmosphere of the star and rotating with it. Such spots could be active regions around the North Pole and the South Pole of a general magnetic dipole field of the star. The P3 periodicity is half the beat of the binary orbital period of the system and the spin period of the giant. The latter is then either 482 or 1790 d. If only one pole is active on the surface of the giant, P3 is the beat period itself, and the spin period is 352 d. It could also be 5000 d if the giant is rotating in a retrograde direction. We briefly compare these findings in the LC of Z Andromedae to similar modulations that were identified in the LC of two other prototype symbiotics, BF Cyg and YY Her. |
format |
Text |
author |
Leibowitz, Elia M. Formiggini, Liliana |
author_facet |
Leibowitz, Elia M. Formiggini, Liliana |
author_sort |
Leibowitz, Elia M. |
title |
Activity cycle of the giant star of Z Andromedae and its spin period |
title_short |
Activity cycle of the giant star of Z Andromedae and its spin period |
title_full |
Activity cycle of the giant star of Z Andromedae and its spin period |
title_fullStr |
Activity cycle of the giant star of Z Andromedae and its spin period |
title_full_unstemmed |
Activity cycle of the giant star of Z Andromedae and its spin period |
title_sort |
activity cycle of the giant star of z andromedae and its spin period |
publisher |
Oxford University Press |
publishDate |
2008 |
url |
http://mnras.oxfordjournals.org/cgi/content/short/385/1/445 https://doi.org/10.1111/j.1365-2966.2008.12847.x |
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South Pole North Pole |
geographic_facet |
South Pole North Pole |
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North Pole South pole |
genre_facet |
North Pole South pole |
op_relation |
http://mnras.oxfordjournals.org/cgi/content/short/385/1/445 http://dx.doi.org/10.1111/j.1365-2966.2008.12847.x |
op_rights |
Copyright (C) 2008, Oxford University Press |
op_doi |
https://doi.org/10.1111/j.1365-2966.2008.12847.x |
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Monthly Notices of the Royal Astronomical Society |
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385 |
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445 |
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