Does the Babcock-Leighton dynamo operate in rapidly rotating solar-type stars? Exploration using a 3D dynamo model at different rotation rates

TL;DR

This study uses a 3D dynamo model to investigate whether the Babcock-Leighton mechanism can sustain magnetic cycles in rapidly rotating solar-type stars, revealing it can operate under certain conditions despite high-latitude starspots.

Contribution

First application of a 3D dynamo model to explore Babcock-Leighton dynamo operation in rapidly rotating stars with varied spot emergence assumptions.

Findings

Cyclic magnetic fields are possible in rapid rotators under most conditions.

Magnetic field geometry shifts to quadrupolar with certain spot rise assumptions.

Irregular magnetic activity occurs in the fastest rotation case with increased spot size and delay.

Abstract

The Babcock-Leighton dynamo, which relies on the generation of a poloidal field through the decay and dispersal of tilted bipolar magnetic regions (BMRs), is a promising paradigm for explaining the features of the solar magnetic cycle. In rapidly rotating stars, BMRs are expected to emerge at high latitudes, which are less efficient in generating the poloidal field due to poor cross-equatorial cancellation. The operation of the Babcock-Leighton dynamo in rapidly rotating stars is therefore questionable. We, for the first time, using a 3D kinematic dynamo model, STABLE, explore this question. By taking large-scale flows from mean-field hydrodynamics models for stars rotating at different speeds, We conduct a series of dynamo simulations in rapidly rotating stars, exploring the following four cases of spot deposition, each based on a different assumption about toroidal flux tube rise: (i) radial rise, (ii) parallel rise to the rotation axis, (iii) parallel rise combined with an increase in Joy's law slope with the stellar rotation rate, and (iv) increasing time delay and spot size. We find cyclic magnetic fields in all cases except case IV of the 1-day rotating star, for which the magnetic field is irregular. For the parallel-rise cases, the magnetic field becomes quadrupolar, and for all other cases, it is dipolar. Our work demonstrates that the Babcock-Leighton dynamo may operate even in rapidly rotating stars with starspots appearing at higher latitudes.