论文标题
一种有效的蒙特卡洛模型，用于放慢光电子的速度。在系外行星气氛中应用于H- $α$
An efficient Monte Carlo model for the slowing down of photoelectrons. Application to H-$α$ in exoplanet atmospheres
论文作者
论文摘要
光电子是行星大气的光电离在光电子上产生的快速电子，驱动大气气体中的转化，这些转化通常受到热电子能量考虑的抑制。转换包括原子和分子的激发和电离，这会影响这些气体的可检测性，并约束转化为热量的入射恒星辐射的比例。为了深入了解这些重要问题，我们建立了一个蒙特卡洛模型，该模型解决了具有任意量H的气体和HE原子和热电子的气体中的光下降。我们的新型多得分方案与相似的工具有所不同，因为它可以有效处理罕见的碰撞通道，例如发生超弹性和无弹性碰撞的低宽容激发原子。该模型已验证，并证明了其性能。此外，我们研究了光电子是否可能影响H-$α$线中的传输光谱在某些系外行星大气中检测到的激发氢H（2）的种群。对于超热的木星HAT-P-32B，我们发现光电子驱动的H（2）的激发在线芯所探测的压力下效率低下，但在线翼形式的大气中变得更加重要（但较为卑鄙）。光电子对通过碰撞去激发或电离破坏H（2）的贡献完全可以忽略不计，这一结论可能会使外部大气层整个。重要的是，光电子在H-$α$线探测的高度处主导了气体电离，即使间接地，H（2）的种群和其他示踪剂（例如亚稳态氦气）可能会影响这一事实。这些激发水平的未来建模应结合光电子驱动的电离。
Photoelectrons, the fast electrons produced in the photoionization of planetary atmospheres, drive transformations in the atmospheric gas that are often inhibited by energy considerations for thermal electrons. The transformations include excitation and ionization of atoms and molecules, which affect the detectability of these gases and constrain the fraction of incident stellar radiation that transforms into heat. To gain insight into these important questions, we build a Monte Carlo model that solves the slowing down of photoelectrons in a gas with arbitrary amounts of H and He atoms and thermal electrons. Our novel multi-score scheme differs from similar tools in that it efficiently handles rare collisional channels, as in the case of low-abundance excited atoms that undergo superelastic and inelastic collisions. The model is validated and its performance demonstrated. Further, we investigate whether photoelectrons might affect the population of the excited hydrogen H(2) detected at some exoplanet atmospheres by transmission spectroscopy in the H-$α$ line. For the ultra-hot Jupiter HAT-P-32b, we find that photoelectron-driven excitation of H(2) is inefficient at the pressures probed by the line core but becomes significant (yet sub-dominant) deeper in the atmosphere where the line wings form. The contribution of photoelectrons to the destruction of H(2) either by collisional deexcitation or ionization is entirely negligible, a conclusion likely to hold for exoplanet atmospheres at large. Importantly, photoelectrons dominate the gas ionization at the altitudes probed by the H-$α$ line, a fact that will likely affect, even if indirectly, the population of H(2) and other tracers such as metastable helium. Future modeling of these excited levels should incorporate photoelectron-driven ionization.
