Stellar Midlife Crises: Challenges and Advances in Simulating Convection and Differential Rotation in Sun-like Stars

Abstract

Low mass, main sequence stars like our Sun exhibit a wide variety of rotational and magnetic states. Observational and theoretical advances have led to a renewed emphasis on understanding the rotational and magnetic evolution of sun-like stars has become a pressing problem in stellar physics. We use global 3D convection and convective dynamo simulations in rotating spherical shells and with realistic stellar stratification to explore the behavior of “middle-aged” stars. We show that for stars with slightly less rotational influence than our Sun a transition occurs from solar-like (fast equator, slow poles) to anti-solar (slow equator, fast poles) differential rotation. We investigate this transition using two different treatments for the upper boundary of our simulations and we hypothesize that this transition from solar-like to anti-solar differential rotation may be responsible for observations of anomalously rapid rotation for stars older than our Sun.

Theory of solar oscillations in the inertial frequency range

“…Global simulations with the solar parameters such as the rotation rate Ω ⊙ and the luminosity L ⊙ tend to produce the socalled anti-solar differential rotation with faster equator and slower poles (e.g., Gastine et al 2013, Käpylä et al 2014, Fan and Fang 2014, Hotta et al 2015c, Karak et al 2015. As we decrease the viscous diffusivity ν, differential rotation changes from solar-like to to the anti-solar profile (Nelson et al 2016). In short, the simulation results tend to deviate from the solar observations as we aim to a more realistic turbulent regime of the Sun.…”