Convection and Differential Rotation Properties of G & K Stars Computed with the ASH Code

TL;DR

This study uses 3D simulations to explore how convection and rotation vary in G- and K-type stars, revealing mass-dependent trends in flow patterns, differential rotation, and circulation structures.

Contribution

It provides new insights into the mass-dependent properties of stellar convection, differential rotation, and meridional circulation in main sequence stars using the ASH code.

Findings

Convective velocities increase with stellar luminosity.

Differential rotation shifts from solar-like to anti-solar with increasing stellar mass.

Meridional circulation patterns evolve from multi-cellular to unicellular with mass increase.

Abstract

The stellar luminosity and depth of the convective envelope vary rapidly with mass for G- and K-type main sequence stars. In order to understand how these properties influence the convective turbulence, differential rotation, and meridional circulation, we have carried out 3D dynamical simulations of the interiors of rotating main sequence stars, using the anelastic spherical harmonic (ASH) code. The stars in our simulations have masses of 0.5, 0.7, 0.9, and 1.1 M_sun, corresponding to spectral types K7 through G0, and rotate at the same angular speed as the sun. We identify several trends of convection zone properties with stellar mass, exhibited by the simulations. The convective velocities, temperature contrast between up- and down-flows, and meridional circulation velocities all increase with stellar luminosity. As a consequence of the trend in convective velocity, the Rossby number (at a fixed rotation rate) increases and the convective turnover timescales decrease significantly with increasing stellar mass. The 3 lowest mass cases exhibit solar-like differential rotation, in a sense that they show a maximum rotation at the equator and minimum at higher latitudes, but the 1.1 M_sun case exhibits anti-solar rotation. At low mass, the meridional circulation is multi-cellular and aligned with the rotation axis; as the mass increases, the circulation pattern tends toward a unicellular structure covering each hemisphere in the convection zone.