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https://stockholmuniversity.zoom.us/j/940229961
The solar magnetic field is generated and sustained through an internal dynamo. In stars, this process is determined by the combined action of turbulent convective motions and the differential rotation profile. It can sometimes lead to magnetic cyclic variabilities, like in the Sun with the 11 years cycle. Traces of magnetic cycles have been detected for other solar-like stars as well, ranging from a few years to a few tens of years. How are these cycles controlled? During their life, the rotation of stars is subject to complex evolution. Recent 3D numerical simulations of solar-like stars show that different regimes of differential rotation can be characterized with the Rossby number. In particular, anti-solar differential rotation (fast poles, slow equator) may exist for high Rossby number (slow rotators). If this regime occurs during the main sequence, and in general for slow rotators, we may wonder how the dynamo process will be impacted, more especially if our Sun is in such a transition. In particular, can slowly rotating stars have magnetic cycles?
I will present a numerical multi-D study with the STELEM and ASH codes to understand the magnetic field generation of solar-like stars under various differential rotation regimes, and focus on the existence of magnetic cycles in a Sun in Time context. We find that short cycles are favoured for small Rossby numbers (fast rotators), and long cycles for intermediate (solar-like) Rossby numbers. Slow rotators (high Rossby number) are found to produce only steady dynamo with no cyclic activity in most cases considered. We further assess the various energy transfers in these stellar dynamos and quantify the amount of magnetic energy available (up to 3% of the stellar luminosity) to power possible surface eruptive events.