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  Shapes of stellar activity cycles

Willamo, T., Hackman, T., Lehtinen, J., Käpylä, M. J., Olspert, N., Viviani, M., et al. (2020). Shapes of stellar activity cycles. Astrophysics & Astronomy, 638: A69. doi:10.1051/0004-6361/202037666.

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Willamo, T., Author
Hackman, T., Author
Lehtinen, Jyri1, Author              
Käpylä, Maarit J.1, 2, Author              
Olspert, N.3, Author
Viviani, Mariangela1, Author              
Warnecke, Jörn1, Author              
Affiliations:
1Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832289              
2Max Planck Research Group and ERC Consolidator Grant: Solar and Stellar Dynamos - SOLSTAR, Max Planck Institute for Solar System Research, Max Planck Society, Justus-von-Liebig-Weg 3, 37077 Göttingen, DE, ou_2265638              
3Max Planck Institute for Solar System Research, Max Planck Society, Justus-von-Liebig-Weg 3, 37077 Göttingen, DE, ou_1125546              

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 Abstract: Context. Magnetic activity cycles are an important phenomenon both in the Sun and other stars. The shape of the solar cycle is commonly characterised by a fast rise and a slower decline, but not much attention has been paid to the shape of cycles in other stars. Aims. Our aim is to study whether the asymmetric shape of the solar cycle is common in other stars as well, and compare the cycle asymmetry to other stellar parameters. We also study the differences in the shape of the solar cycle, depending on the activity indicator that is used. The observations are also compared to simulated activity cycles. Methods. We used the chromospheric Ca II H&K data from the Mount Wilson Observatory HK Project. In this data set, we identified 47 individual cycles from 18 stars. We used the statistical skewness of a cycle as a measure of its asymmetry, and compared this to other stellar parameters. A similar analysis has been performed for magnetic cycles extracted from direct numerical magnetohydrodynamic simulations of solar-type convection zones. Results. The shape of the solar cycle (fast rise and slower decline) is common in other stars as well, although the Sun seems to have particularly asymmetric cycles. Cycle-to-cycle variations are large, but the average shape of a cycle is still fairly well represented by a sinusoid, although this does not take its asymmetry into account. We find only slight correlations between the cycle asymmetry and other stellar parameters. There are large differences in the shape of the solar cycle, depending on the activity indicator that is used. The simulated cycles differ in the symmetry of global simulations that cover the full longitudinal range and are therefore capable of exciting non-axisymmetric large-scale dynamo modes, and wedge simulations that cover a partial extent in longitude, where only axisymmetric large-scale modes are possible. The former preferentially produce positive and the latter negative skewness.

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Language(s): eng - English
 Dates: 2020
 Publication Status: Published in print
 Pages: -
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 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/202037666
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Title: Astrophysics & Astronomy
  Other : Astrophys. Astron.
Source Genre: Journal
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Publ. Info: Berlin : Springer-Verlag
Pages: - Volume / Issue: 638 Sequence Number: A69 Start / End Page: - Identifier: ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219