论文标题
边界层绕开式积聚：一个未磁化的行星通过其圆盘旋转的速度有多快？
Boundary Layer Circumplanetary Accretion: How Fast Could an Unmagnetized Planet Spin Up Through Its Disk?
论文作者
论文摘要
预计气体巨型行星将通过圆周磁盘积聚大部分质量。如果行星不被渗透并最初缓慢旋转，则它将通过径向狭窄的边界层吸收气体并迅速向上旋转。边界层的径向扩大随着行星的旋转而降低了积聚气体的特定角动量，从而使行星能够找到末端旋转速率短于断裂速率。在这里，我们使用轴对称粘性水动力模拟来量化从其圆周磁盘中积聚的行星的末端旋转速率。对于一个等温行星盘系统，磁盘尺度高度$ h/r = 0.1 $在行星表面附近，请旋转开关以在70 \％至80 \％之间旋转，占行星断裂角速度的旋转。在与垂直平均模型的定性区别中 - 旋转可以与质量积聚共存 - 我们观察到\ emph {decretion}伴随丢失角动量的解决方案。临界自旋速率取决于行星附近的磁盘厚度。对于在行星附近的磁盘尺度高度为$ h/r = 0.15 $的等温系统，临界旋转速率下降到行星断裂角速度的60 \％至70 \％之间。在边界层外部的磁盘中，我们确定了子午循环流，这些流动流不稳定且在整个平面中是不对称的。模拟的流足够强，可以在早期卫星形成中垂直重新分布固体物质。我们讨论当与磁盘对原始球星的光谱和变异性研究结合时，如何确定磁性和非磁性过程在设置巨型行星旋转中的作用。
Gas giant planets are expected to accrete most of their mass via a circumplanetary disk. If the planet is unmagnetized and initially slowly rotating, it will accrete gas via a radially narrow boundary layer and rapidly spin up. Radial broadening of the boundary layer as the planet spins up reduces the specific angular momentum of accreted gas, allowing the planet to find a terminal rotation rate short of the breakup rate. Here, we use axisymmetric viscous hydrodynamic simulations to quantify the terminal rotation rate of planets accreting from their circumplanetary disks. For an isothermal planet-disk system with a disk scale height $h/r =0.1$ near the planetary surface, spin up switches to spin down at between 70\% and 80\% of the planet's breakup angular velocity. In a qualitative difference from vertically-averaged models -- where spin down can co-exist with mass accretion -- we observe \emph{decretion} accompanying solutions where angular momentum is being lost. The critical spin rate depends upon the disk thickness near the planet. For an isothermal system with a disk scale height of $h/r = 0.15$ near the planet, the critical spin rate drops to between 60\% and 70\% of the planet's breakup angular velocity. In the disk outside the boundary layer, we identify meridional circulation flows, which are unsteady and instantaneously asymmetric across the mid-plane. The simulated flows are strong enough to vertically redistribute solid material in early-stage satellite formation. We discuss how extrasolar planetary rotation measurements, when combined with spectroscopic and variability studies of protoplanets with circumplanetary disks, could determine the role of magnetic and non-magnetic processes in setting giant planet spins.
