Large-scale stellar dynamos

Recent spectropolarimetric observations of low-mass stars show that large-scale components of their magnetic fields can exhibit cyclic variations or reversals. This magnetic activity affects detection of exoplanets and estimation of their masses, and so its modelling is particularly important. In convective stellar envelopes, magnetic fields are created through dynamo action - systematic stretching and twisting of magnetic field lines by helical convective vortices. It is yet however unclear how low-mass stars, with their strong convective turbulence and relatively slow rotation, are able to maintain coherent large-scale magnetic activity. In this talk, I will discuss the physical mechanisms that allow magnetic flux to accumulate at large scales in both turbulent and strongly stratified models of stellar convection. In such models, a highly turbulent convective layer is formed at the surface while the deep flow interiors remain rotationally constrained. Using direct numerical simulations of such flows, I explore the mechanisms that allow small-scale magnetic flux, generated by small-scale turbulence in the outer regions with low density, to accumulate in more quiescent inner regions. I also explore magnetic variations such as polarity reversals that can be responsible for diversity of magnetic topology observed in low-mass stars. (Pinçon et al., 2024)