论文标题

气态动力学怪胎的偏心演变

Eccentricity Evolution in Gaseous Dynamical Friction

论文作者

Szölgyén, Ákos, MacLeod, Morgan, Loeb, Abraham

论文摘要

我们分析阻力力如何修改通过扩展气体分布移动的对象的轨道。我们考虑流体动力(表面积)阻力和动力学摩擦(重力)阻力如何驱动轨道偏心的演变。尽管流体动力阻力会导致偏心轨道变得更加圆形,但动态摩擦阻力会导致轨道变得更加偏心。我们开发了一个半分析模型,该模型通过比较在Periapse和Apoapse上应用于轨道的总工作和扭矩来准确预测这些变化。我们使用径向幂律密度剖面的玩具模型,$ρ\ propto r^{ - γ} $,以确定有一个关键的$γ= 3 $功率指数,这使动力摩擦中的偏心率分开:轨道在$γ<3 $中变得更偏心,并以$γ>> 3 $循环。我们将这些发现应用于像木星一样的星球的中继中,并将其置于其宿主星的信封中。恒星的静液压信封是由肢体附近的陡峭密度梯度和内部较浅的梯度定义的。在气态动力学摩擦的影响下,插入物体的轨道将首先降低偏心率,然后增加。描绘这些机制的临界分离由局部密度斜率预测,并线性取决于多环反应指数。更广泛地说,我们的发现表明,二进制系统可能会常规地从具有非零偏心率的共同包膜阶段出现,这些偏心率受到驱动轨道拧紧的动力摩擦力而激发的。

We analyse how drag forces modify the orbits of objects moving through extended gaseous distributions. We consider how hydrodynamic (surface area) drag forces and dynamical friction (gravitational) drag forces drive the evolution of orbital eccentricity. While hydrodynamic drag forces cause eccentric orbits to become more circular, dynamical friction drag can cause orbits to become more eccentric. We develop a semi-analytic model that accurately predicts these changes by comparing the total work and torque applied to the orbit at periapse and apoapse. We use a toy model of a radial power-law density profile, $ρ\propto r^{-γ}$, to determine that there is a critical $γ= 3$ power index which separates the eccentricity evolution in dynamical friction: orbits become more eccentric for $γ< 3$ and circularize for $γ> 3$. We apply these findings to the infall of a Jupiter-like planet into the envelope of its host star. The hydrostatic envelopes of stars are defined by steep density gradients near the limb and shallower gradients in the interior. Under the influence of gaseous dynamical friction, an infalling object's orbit will first decrease in eccentricity, then increase. The critical separation that delineates these regimes is predicted by the local density slope and is linearly dependent on polytropic index. More broadly, our findings indicate that binary systems may routinely emerge from common envelope phases with non-zero eccentricities that were excited by the dynamical friction forces that drove their orbital tightening.

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