Motivated by the recent surge in interest concerning white dwarf (WD) planets, this work presents the first numerical exploration of WD-driven atmospheric escape, whereby the high-energy radiation from a hot/young WD can trigger the outflow of the hydrogen–helium envelope for close-in planets. As a pilot investigation, we focus on two specific cases: a gas giant and a sub-Neptune-sized planet, both orbiting a rapidly cooling WD with mass M* = 0.6 M⊙ and separation a = 0.02 au. In both cases, the ensuing mass outflow rates exceed 1014 g s−1 for WD temperatures greater than TWD ≳ 50,000 K. At TWD ≃ 18,000 K (22,000 K), the sub-Neptune (gas giant) mass outflow rate approaches 1012 g s−1, i.e., comparable to the strongest outflows expected from close-in planets around late main-sequence stars. Whereas the gas giant remains virtually unaffected from an evolutionary standpoint, atmospheric escape may have sizable effects for the sub-Neptune, depending on its dynamical history, e.g., assuming that the hydrogen–helium envelope makes up 1% (4%) of the planet mass, the entire envelope would be evaporated away so long as the planet reaches 0.02 au within the first 230 Myr (130 Myr) of the WD formation. We discuss how these results can be generalized to eccentric orbits with effective semimajor axis , which receive the same orbit-averaged irradiation. Extended to a much broader parameter space, this approach can be exploited to model the expected demographics of WD planets as a function of their initial mass, composition, and migration history, as well as their potential for habitability.

中文翻译：

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通过冷却白矮星来蒸发近距离的亚海王星

受最近人们对白矮星 (WD) 行星的兴趣激增的推动，这项工作首次对白矮星 (WD) 驱动的大气逃逸进行数值探索，其中来自热/年轻 WD 的高能辐射可以触发氢-氦的流出近距离行星的包络线。作为试点研究，我们重点关注两个具体案例：一颗气态巨行星和一颗亚海王星大小的行星，两者都围绕一个快速冷却的 WD 运行，质量 M* = 0.6 M⊙，间距 a = 0.02 au。在这两种情况下，当 WD 温度大于 TWD ≳ 50,000 K 时，随后的质量流出速率超过 1014 gs−1。在 TWD ≃ 18,000 K (22,000 K) 时，亚海王星（气态巨星）质量流出速率接近 1012 gs−1 ，即与后期主序恒星周围的近距离行星预期的最强流出量相当。虽然从进化的角度来看，这颗气态巨行星实际上并未受到影响，但大气逃逸可能会对亚海王星产生相当大的影响，具体取决于它的动力学历史，例如，假设氢-氦包层占行星的 1% (4%)质量，只要行星在 WD 形成的前 230 迈尔 (130 Myr) 内达到 0.02 天文单位，整个包层就会被蒸发掉。我们讨论如何将这些结果推广到具有有效半长轴的偏心轨道，这些轨道接受相同的轨道平均辐射。扩展到更广泛的参数空间，可以利用这种方法来模拟 WD 行星的预期人口统计数据，作为其初始质量、组成和迁移历史以及宜居潜力的函数。