Common dynamo scaling in slowly rotating young and evolved stars

Jyri J. Lehtinen*, Federico Spada, Maarit J. Käpylä, Nigul Olspert, Petri J. Käpylä

*Corresponding author for this work

Research output: Contribution to journalLetterScientificpeer-review

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Abstract

One interpretation of the activity and magnetism of late-type stars is that these both intensify with decreasing Rossby number up to a saturation level1–3, suggesting that stellar dynamos depend on both rotation and convective turbulence4. Some studies have claimed, however, that rotation alone suffices to parametrize this scaling adequately5,6. Here, we tackle the question of the relevance of turbulence to stellar dynamos by including evolved, post-main-sequence stars in the analysis of the rotation–activity relation. These stars rotate very slowly compared with main-sequence stars, but exhibit similar activity levels7. We show that the two evolutionary stages fall together in the rotation–activity diagram and form a single sequence in the unsaturated regime in relation only to Rossby numbers derived from stellar models, confirming earlier preliminary results that relied on a more simplistic parametrization of the convective turn-over time8,9. This mirrors recent results of fully convective M dwarfs, which likewise fall on the same rotation–activity sequence as partially convective solar-type stars10,11. Our results demonstrate that turbulence plays a crucial role in driving stellar dynamos and suggest that there is a common turbulence-related dynamo mechanism explaining the magnetic activity of all late-type stars.

Original languageEnglish
JournalNature Astronomy
DOIs
Publication statusE-pub ahead of print - 1 Jan 2020
MoE publication typeA1 Journal article-refereed

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  • Projects

    UniSDyn: Building up a Unified Theory of Stellar Dynamos

    Käpylä, M., Rheinhardt, M. & Pekkilä, J.

    01/01/202031/12/2024

    Project: EU: ERC grants

    Press / Media

    Turbulent convection at the heart of stellar activity

    Maarit Käpylä

    09/03/2020

    3 items of Media coverage

    Press/Media: Media appearance

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