From solar-like to antisolar differential rotation in cool stars

Abstract

Stellar differential rotation can be separated into two main regimes: solar-like when the equator rotates faster than the poles and antisolar when the polar regions rotate faster than the equator. We investigate the transition between these two regimes with 3D numerical simulations of rotating spherical shells. We conduct a systematic parameter study which also includes models from different research groups. We find that the direction of the differential rotation is governed by the contribution of the Coriolis force in the force balance, independently of the model setup (presence of a magnetic field, thickness of the convective layer, density stratification). Rapidly rotating cases with a small Rossby number yield solar-like differential rotation, while weakly rotating models sustain antisolar differential rotation. Close to the transition, the two kinds of differential rotation are two possible bistable states. This study provides theoretical support for the existence of antisolar differential rotation in cool stars with large Rossby numbers.

Laboratory-numerical models of rapidly rotating convection in planetary cores

“…Aurnou 2007;Gastine et al 2013Gastine et al , 2014. However, in our rotating convection experiments, in which convective heat transfer is controlled by distinctly smaller scale motions, the data are not well collapsed by this system-scale parameter.…”

“…It has been argued that the convection regime dominated by rotation extends from the onset of rotating convection at Ra C near to where the convective Rossby number is of order unity, Ro c 1 (e.g. Gilman 1977;Aurnou et al 2007;Zhong & Ahlers 2010;Gastine et al 2013Gastine et al , 2014Stevens et al 2013). This predicts that the steep heat transfer scaling regime will extend over the range Ra C Ra E −2 Pr.…”

Antisolar differential rotation of the K1-giantσ Geminorum revisited

“…It is not understood, however, what kind of general relationship exists in close binaries between the characteristics of the DR and other astrophysical parameters (cf., e.g., Dunstone et al 2008;Holzwarth & Schüssler 2003; but see also Gastine et al 2014).…”

Meridional Circulation in Solar and Stellar Convection Zones

“…In other words, convective velocity scales increase while length scales decrease. Near the solar/anti-solar transition, Gastine et al (2014) and Käpylä et al (2014) also find that the DR exhibits bistability, with both solar and anti-solar regimes possible, depending on initial conditions and hysteresis.…”