Retarded Stellar Dynamo in Tidally Deformed M Dwarfs

Abstract

Current studies of stellar dynamos primarily focus on spherical stars, leaving their behavior in distorted stars largely unexplored. We utilize stars of varying distortions to examine the relation between stellar cycle periods ($P_{\mathrm{cyc}}$) and rotational periods ($P_{\mathrm{rot}}$), which are closely linked to dynamo processes. By analyzing a sample of tidally distorted M dwarfs in cataclysmic variables, we identify an anti-correlation between $P_{\mathrm{cyc}}$ and $P_{\mathrm{rot}}$, in contrast to the lack of such a relation in single M dwarfs. This means that stars with greater deformation have longer cycle periods, suggesting variations in dynamo behavior under non-spherical geometries. Our numerical simulations further reveal that, the thermal convection weakens in highly distorted stars, and subsequently, the differential rotation is also reduced. These effects may lengthen the conversion timescale between poloidal and toroidal magnetic fields, potentially explaining the newly discovered $P_{\mathrm{cyc}}$-$P_{\mathrm{rot}}$ relation in cataclysmic variables.

7 figures and 1 table in main text; 5 tables and 1 figure in supplement. Accepted by SCPMA

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