Simulations of fully convective M dwarfs: dynamo action with varying magnetic Prandtl numbers

M dwarfs are low-mass main-sequence stars, the most numerous type of stars in the solar neighbourhood, which are known to have significant magnetic activity. The aim of this work is to explore the dynamo solutions and magnetic fields of fully convective M dwarfs with varying magnetic Prandtl numbers Pr_M, and a rotation period (P_rot) of 43 days. Pr_M is known to play an important role in the dynamo action; dynamos for low-Pr_M and large-Pr_M have very different properties. We performed three-dimensional magnetohydrodynamical (MHD) numerical simulations with the ``star-in-a- box'' model using stellar parameters for an M5 dwarf with 0.21 M_⊙. We found that the dynamo solutions are sensitive to Pr_. The simulations at this rotation period present periodic cycles of the large-scale magnetic field up to Pr_M ≤ 2; for higher values the cycles disappear and irregular solutions to arise. Our results are consistent with previous studies and suggest that the dynamos operating in fully convective stars behave similarly as those in partially convective stars.