A Knee-Point in the Rotation-Activity Scaling of Late-type Stars with a Connection to Dynamo Transitions

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Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2021-04-01
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Mcode
Degree programme
Language
en
Pages
8
Series
Astrophysical Journal, Volume 910, issue 2
Abstract
The magnetic activity of late-type stars is correlated with their rotation rates. Up to a certain limit, stars with smaller Rossby numbers, defined as the rotation period divided by the convective turnover time, have higher activity. A more detailed look at this rotation-activity relation reveals that, rather than being a simple power law relation, the activity scaling has a shallower slope for the low-Rossby stars than for the high-Rossby ones. We find that, for the chromospheric CaII H&K activity, this scaling relation is well modelled by a broken two-piece power law. Furthermore, the knee-point of the relation coincides with the axisymmetry to non-axisymmetry transition seen in both the spot activity and surface magnetic field configuration of active stars. We interpret this knee-point as a dynamo transition between dominating axi- and non-axisymmetric dynamo regimes with a different dependence on rotation and discuss this hypothesis in the light of current numerical dynamo models.
Description
| openaire: EC/H2020/824135/EU//SOLARNET | openaire: EC/H2020/818665/EU//UniSDyn
Keywords
Astrophysics - Solar and Stellar Astrophysics
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Citation
Lehtinen, J J, Käpylä, M J, Olspert, N & Spada, F 2021, ' A Knee-Point in the Rotation-Activity Scaling of Late-type Stars with a Connection to Dynamo Transitions ', The Astrophysical Journal, vol. 910, no. 2, 110 . https://doi.org/10.3847/1538-4357/abe621