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https://stockholmuniversity.zoom.us/j/530682073
https://arxiv.org/abs/2012.01259
Low mass stars below about 0.35 solar mass or spectral class M3.5 are fully convective. According to stellar structure and evolution models the transition to full convection is abrupt in that the minimum size of a stable radiative core in the lightest partially convective stars is roughly 40% of stellar radius. This is interesting from a dynamo-theoretic perspective because fully convective stars do not have a tachocline, a layer of strong shear at the interface of radiative and convective zones, which plays a crucial role in some models of the solar dynamo. This could mean that the dynamos in fully convective stars are fundamentally different from those in partially convective stars. However, no unambiguous break in magnetic activity indicators has been observed accross the transition to full convection to date. Thus it is of great interest for stellar dynamo theory to study the magnetic field generation in fully convective stars in comparison to corresponding partially convective stars.
In this talk I will present results from a set of modest resolution simulations of a 0.2 solar mass M5 dwarf made with an updated version of the star-in-a-box model introduced in Dobler et al. (2006, ApJ, 638, 336). This setup allows the full star to be modeled in Cartesian coordinates without having to deal with coordinate singularities. The set of runs covers rotation periods between 4.3 and 430 days corresponding to Coriolis (inverse Rossby) numbers between 0.7 and more than 300. The current results show that transitions of differential rotation and large-scale dynamo solutions occur very similarly as in partially convective cases which could suggests a common origin of magnetism in fully and partially convective stars.