Towards understanding dynamo action in M dwarfs

Abstract

Recent progress in observational studies of magnetic activity in M dwarfs urgently requires support from ideas of stellar dynamo theory. We propose a strategy to connect observational and theoretical studies. In particular, we suggest four magnetic configurations that appear relevant to dwarfs from the viewpoint of the most conservative version of dynamo theory, and discuss observational tests to identify the configurations observationally. As expected, any such identification contains substantial uncertainties. However the situation in general looks less pessimistic than might be expected. Several identifications between the phenomenology of individual stars and dynamo models are suggested. Remarkably, all models discussed predict substantial surface magnetic activity at rather high stellar latitudes. This prediction looks unexpected from the viewpoint of our experience observing the Sun (which of course differs in some fundamental ways from these late-type dwarfs). We stress that a fuller understanding of the topic requires a long-term (at least 15 years) monitoring of M dwarfs by Zeeman-Doppler imaging.

8 pages, 4 figures, accepted by MNRAS

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• Strong dipole magnetic fields in fast rotating fully convective stars
• Magnetic cycles in a dynamo simulation of fully convective M-star Proxima Centauri
• Surprisingly different starspot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB
• Evolution of solar and stellar dynamo theory
• Extending Optical Flare Models to the UV: Results from Comparing of TESS and GALEX Flare Observations For M Dwarfs
• Nonlinear regimes in mean-field full-sphere dynamo
• Wavelet analysis of the long-term activity of V833 Tau
• Modelling the environment around five ultracool dwarfs via the radio domain
• A short and sudden increase of the magnetic field strength and the accompanying spectral variability in the O9.7V star HD54879
• Cycles on the Solar-Type Stars and Cooler Dwarfs
• Magnetic fields of low-mass main sequences stars: Nonlinear dynamo theory and mean-field numerical simulations
• The Solar Neighborhood LII: M Dwarf Twin Binaries -- Presumed Identical Twins Appear Fraternal in Variability, Rotation, H$\alpha$, and X-rays
• The Solar Neighborhood. LV. M Dwarf Twin Binaries -- One in Five Twin Sibling Pairs Are Mismatched in Activity and/or Rotation
• CARMENES input catalog of M dwarfs VI. A time-resolved Ca II H&K catalog from archival data