On differential rotation and overshooting in solar-like stars

Abstract

We seek to characterize how the change of global rotation rate influences the overall dynamics and large scale flows arising in the convective envelopes of stars covering stellar spectral types from early G to late K. We do so through numerical simulations with the ASH code, where we consider stellar convective envelopes coupled to a radiative interior with various global properties. As solar-like stars spin down over the course of their main sequence evolution, such change must have a direct impact on their dynamics and rotation state. We indeed find that three main states of rotation may exist for a given star: anti-solar-like (fast poles, slow equator), solar-like (fast equator, slow poles), or a cylindrical rotation profile. Under increasingly strict rotational constraints, the latter profile can further evolve into a Jupiter-like profile, with alternating prograde and retrograde zonal jets. We have further assessed how far the convection and meridional flows overshoot into the radiative zone and investigated the morphology of the established tachocline. Using simple mixing length arguments, we are able to construct a scaling of the fluid Rossby number $R_{of}=\tilde{\omega }/2{\Omega }_{\ast }\sim \tilde{v}/2{\Omega }_{\ast }{R}_{\ast }$, which we calibrate based on our 3-D ASH simulations. We can use this scaling to map the behavior of differential rotation versus the global parameters of stellar mass and rotation rate. Finally, we isolate a region on this map ($R_{of}\gtrsim 1.5-2$) where we posit that stars with an anti-solar differential rotation may exist in order to encourage observers to hunt for such targets.

Published in ApJ, 836, 192. 22 Colour figures, 28 pages. ${}^1$ AIM/SAp, CEA-Saclay, 91191 Gif-sur-Yvette, France, ${}^2$ Physics and Astronomy, Univ. of Exeter, Exeter, UK, ${}^3$ Astronomy Dept., Univ. of Montreal, Montreal, Canada, ${}^4$ LASP and Dept. of Astrophysical & Planetary Sciences, Univ. of Colorado, Boulder, USA, ${}^5$ JILA, Univ. of Colorado, Boulder, USA

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• Surprisingly different starspot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB
• Extreme value statistics for two-dimensional convective penetration in a pre-Main Sequence star
• A model of rotating convection in stellar and planetary interiors: I - convective penetration
• Origin and evolution of magnetic fields in PMS stars : influence of rotation and structural changes
• Activity time series of old stars from late F to early K. I. Simulating radial velocity, astrometry, photometry, and chromospheric emission
• Latitudinal differential rotation in the solar analogues 16 Cyg A and B
• Internal magnetic fields, spin-orbit coupling, and orbital period modulation in close binary systems
• Magnetic geometry and surface differential rotation of the bright Am star Alhena A
• Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry
• Predicting the Rossby number in convective experiments
• The first Doppler imaging of the active binary prototype RS Canum Venaticorum
• Convective Differential Rotation in Stars and Planets I: Theory
• The partial ionisation zone of heavy elements in F-stars: a study on how it correlates with rotation
• Convective Differential Rotation in Stars and Planets II: Observational and Numerical Tests
• Differential Rotation in Convective Envelopes: Constraints from Eclipsing Binaries
• Upward Overshooting in Turbulent Compressible Convection. III. Calibrate Parameters for One-dimensional Reynolds Stress Model
• Simulating the outer layers of rapidly rotating stars