来自近距离太阳系外行星的各向异性风
Anisotropic winds from close-in extra-solar planets
摘要：
我们提出了两维流体动力学模型的热驱动风高度辐射，密切的太阳系外行星。我们采用了一个非常简单的处理的辐射加热过程中的风的基础，而不是集中在不同的属性之间的流出在多维相比，球对称模型计算相同的方法。对于高温（T > 2 x 10^{4} K）或高度电离的气体，我们发现在行星表面上方形成了强（超音速）极流，在夜侧产生弱激波和外流。与具有相同参数的球对称风相比，在多维空间中，昼侧的声波表面更接近行星表面，总质量损失率几乎减少了四分之一。我们还计算了相互作用的行星风和恒星风的稳态结构。两种风都以终止激波结束，抛物线接触间断覆盖在行星上，将两种激波分开。行星风的终止激波和风中的音速表面被很好地分离，因此行星的质量损失率基本上不受影响。然而，行星风被限制在接触不连续性所限定的小体积内，大大增强了行星附近的柱密度，这对于解释过境行星周围气体形成的吸收线的观测可能很重要。
英文摘要：
We present two-dimensional hydrodynamic models of thermally driven winds from highly irradiated, close-in extra-solar planets. We adopt a very simple treatment of the radiative heating processes at the base of the wind, and instead focus on the differences between the properties of outflows in multidimensions in comparison to spherically symmetric models computed with the same methods. For hot (T > 2 x 10^{4} K) or highly ionized gas, we find strong (supersonic) polar flows are formed above the planet surface which produce weak shocks and outflow on the night-side. In comparison to a spherically symmetric wind with the same parameters, the sonic surface on the day-side is much closer to the planet surface in multidimensions, and the total mass loss rate is reduced by almost a factor of four. We also compute the steady-state structure of interacting planetary and stellar winds. Both winds end in a termination shock, with a parabolic contact discontinuity which is draped over the planet separating the two shocked winds. The planetary wind termination shock and the sonic surface in the wind are well separated, so that the mass loss rate from the planet is essentially unaffected. However, the confinement of the planetary wind to the small volume bounded by the contact discontinuity greatly enhances the column density close to the planet, which might be important for the interpretation of observations of absorption lines formed by gas surrounding transiting planets.
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