Differential rotation and meridional flow of Arcturus

TL;DR

This study models Arcturus's internal rotation and flow patterns, revealing weaker surface shear than the Sun and conditions unfavorable for a circulation-driven dynamo, thus informing stellar magnetic activity theories.

Contribution

It provides the first mean-field model of Arcturus's internal rotation and flow, comparing its dynamo conditions to the Sun's and assessing magnetic activity potential.

Findings

Arcturus exhibits solar-type surface rotation with reduced shear.

Rotation increases monotonically with depth throughout the convection zone.

Conditions are unfavorable for a circulation-dominated dynamo on Arcturus.

Abstract

The spectroscopic variability of Arcturus hints at cyclic activity cycle and differential rotation. This could provide a test of current theoretical models of solar and stellar dynamos. To examine the applicability of current models of the flux transport dynamo to Arcturus, we compute a mean-field model for its internal rotation, meridional flow, and convective heat transport in the convective envelope. We then compare the conditions for dynamo action with those on the Sun. We find solar-type surface rotation with about 1/10th of the shear found on the solar surface. The rotation rate increases monotonically with depth at all latitudes throughout the whole convection zone. In the lower part of the convection zone the horizontal shear vanishes and there is a strong radial gradient. The surface meridional flow has maximum speed of 110 m/s and is directed towards the equator at high and towards the poles at low latitudes. Turbulent magnetic diffusivity is of the order $10^{15}$--$10^{16} {\rm cm^2/s}$. The conditions on Arcturus are not favorable for a circulation-dominated dynamo.