Physically motivated heat conduction treatment in simulations of solar-like stars: effects on dynamo transitions

TL;DR

This study investigates how implementing physically motivated heat conduction, using Kramers opacity law, affects the simulation of solar-like stars, leading to improved dynamo behavior and better alignment with observational data in certain regimes.

Contribution

The paper introduces a heat conduction treatment based on Kramers law into stellar simulations, which alters dynamo transition points and wave propagation, improving agreement with observations in some aspects.

Findings

Shifted the axi- to non-axisymmetric transition to higher rotation rates

Observed change in the propagation direction of azimuthal dynamo waves to include prograde waves

Improved dynamo solutions in faster rotation regimes, aligning better with observations

Abstract

Context. Results from global magnetoconvection simulations of solar-like stars are at odds with observations in many respects: They show a surplus of energy in the kinetic power spectrum at large scales, anti-solar differential rotation profiles, with accelerated poles and a slow equator, for the solar rotation rate, and a transition from axi- to non-axisymmetric dynamos at a much lower rotation rate than what is observed. Even though the simulations reproduce the observed active longitudes in fast rotators, their motion in the rotational frame (the so-called azimuthal dynamo wave, ADW) is retrograde, in contrast to the prevalent prograde motion in observations. Aims. We study the effect of a more realistic treatment of heat conductivity in alleviating the discrepancies between observations and simulations. Methods. We use physically-motivated heat conduction, by applying Kramers opacity law, on a semi-global spherical setup describing convective envelopes of solar-like stars, instead of a prescribed heat conduction profile from mixing-length arguments. Results. We find that some aspects of the results now better correspond to observations: The axi- to non-axisymmetric transition point is shifted towards higher rotation rates. We also find a change in the propagation direction of ADWs so that also prograde waves are now found. The transition from anti-solar to solar-like rotation profile, however, is also shifted towards higher rotation rates, leaving the models into an even more unrealistic regime. Conclusions. Although a Kramers-based heat conduction does not help in reproducing the solar rotation profile, it does help in the faster rotation regime, where the dynamo solutions now match better with observations.