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Accretion of Gas Giants Constrained by the Tidal Barrier
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  • Ya-Ping Li,
  • Yixian Chen,
  • Douglas Lin,
  • Xiaojia Zhang
Ya-Ping Li
Los Alamos National Laboratory
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Yixian Chen
Tsinghua University

Corresponding Author:[email protected]

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Douglas Lin
UC Santa Cruz
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Xiaojia Zhang
University of Hong Kong
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After protoplanets have acquired sufficient mass to open partial gaps in their natal protostellar disks, residual gas continues to diffuse onto some horseshoe streamlines under effect of viscous dissipation, and meander in and out of the planets’ Hill sphere. Inside the Hill sphere, the horseshoe streamlines intercept gas flow in circumplanetary disks. The host stars’ tidal perturbation induce a barrier across the converging streamlines’ interface. Viscous transfer of angular momentum across this tidal barrier determines the rate of mass diffusion from the horseshoe streamlines onto the circumplanetary disks, and eventually the accretion rate onto the protoplanets. We carry out a series of numerical simulations to test the influence of this tidal barrier on super-thermal planets. In weakly viscous disks, protoplanets’ accretion rate steeply decreases with their masses above the thermal limit. As their growth time scale exceeds the gas depletion time scale, their masses reach asymptotic values comparable to that of Jupiter. In relatively thick and strongly viscous disks, protoplanets’ asymptotic masses exceed several times that of Jupiter. Such massive protoplanets strongly excite the eccentricity of nearby horseshoe streamlines, destabilize orderly flow, substantially enhance the diffusion rate across the tidal barrier, and elevate their growth rate until their natal disk is severely depleted. Based on the upper fall-off in the observe mass distribution of known exoplanets, we suggest their natal disks had relatively low viscosity (α ∼ 10−3), modest thickness (H/R ∼ 0.03 − 0.05), and limited masses (comparable to that of minimum mass solar nebula model).
06 Jan 2021Published in The Astrophysical Journal volume 906 issue 1 on pages 52. 10.3847/1538-4357/abc883