Predicting the length of magnetic cycles in late-type stars

II. Solar and stellar butterfly diagrams: A forked dynamo model

¹ European Space Astronomy Centre (ESAC) European Space Agency (ESA), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
² Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain

^★ Corresponding author.

Received: 31 March 2025
Accepted: 3 June 2025

Abstract

Aims. We present a one-dimensional dynamo model, along with its application to a sample of late-type stars with well-determined activity cycles.

Methods. In addition to reproducing the observed dependence of the cycle period, P_cyc, on the stellar rotation period, P_rot, for the stars in the sample, the model also reproduces the main properties of the solar butterfly diagram and generates possible magnetic diagrams for the other stars.

Results. The adopted interface dynamo model, which incorporates the essential magnetic generation processes, needs to be modified into a ‘forked dynamo’ at high latitudes to generate strong magnetic fields near the equator. This simple model offers an intuitive view of the dynamo mechanisms that might be operating in the stellar interiors.