Spectral appearance of the planetary-surface accretion shock: Global spectra and hydrogen-line profiles and fluxes
Yuhiko Aoyama, Gabriel-Dominique Marleau, Christoph Mordasini, Masahiro Ikoma
备注：
20 pages, 8 figures (main text) + 14 pages, 7 figures (Appendix + references), re-submitted to ApJ. V.3: Model details moved to Appendix, Sect. 6.5 simplified, Appendix A on Storey & Hummer (1995) corrected, small changes. Results unchanged. Fits to radii and Teff's of accreting planets at https://github.com/gabrielastro/St-Moritz (in gnuplot/IDL/python)
Hydrogen-line emission from an accretion shock has recently been observed at planetary-mass objects. Our previous work predicted the shock spectrum and luminosity for a shock on the circumplanetary disc. We extend this to the planet-surface shock. We calculate the global spectral energy distribution (SED) of accreting planets by combining our model emission spectra with photospheric SEDs, and predict the line-integrated flux for several hydrogen lines, especially H alpha, but also H beta, Pa alpha, Pa beta, Pa gamma, Br alpha, and Br gamma. We apply our non-equilibrium emission model to the surface accretion shock for a wide range of accretion rates Mdot and masses M_p . Fits to formation calculations provide radii and effective temperatures. Extinction by the surrounding material is neglected, which is arguably often relevant. We find that the line luminosity increases monotonically with Mdot and M_p , depending mostly on Mdot and weakly on M_p for the relevant range of parameters. The Lyman, Balmer, and Paschen continua can exceed the photosphere. The H beta line is fainter by 0 to 1 dex than H alpha, whereas other lines are weaker (by 1 to 3 dex). Shocks on the planet or the CPD surface are distinguishable at very high spectral resolution, but the planet surface shock likely dominates if both are present. Applied to recent non-detections of H alpha, our models imply looser constraints on the Mdot of putative planets than when extrapolating fits from the stellar regime. These hydrogen-line luminosity predictions are useful for interpreting (non-)detections of accreting planets.
Evolution of Earth-like extrasolar planetary atmospheres: Assessing the atmospheres and biospheres of early Earth analog planets with a coupled atmosphere biogeochemical model
XUV Radiation from A-stars: Implications for Ultra-hot Jupiters
极度辐射，靠近早期恒星的行星可能容易发生强烈的大气逃逸。我们回顾的文献表明，X射线到光学测量表明，对于中等质量的恒星（IMS）比$\approx$ 8250 K冷，X射线和EUV（XUV）通量平均显着高于太阳类恒星，而对于较热的IMS，由于缺乏表面对流，它是相反的。我们构建光谱能量分布的原型IMS，比较他们的太阳能。与上层行星大气加热相关的XUV通量在较冷的IMS中最高，在较热的IMS中最低，而UV通量随着恒星温度的增加而增加。我们量化的影响，这一特点的恒星通量上的质量损失的近距离行星通过模拟的大气中的行星轨道EUV明亮（WASP-33）和EUV微弱（KELT-9）的A型恒星。对于KELT-9 b，我们发现，由于恒星紫外线和光学光的吸收加热引起的大气膨胀驱动器的质量损失率为$\approx$ 10 $^{11}$ g s $^{-1}$，而恒星XUV辐射的吸收加热引起的质量损失率为$\approx$ 10 $^{10}$ g s $^{-1}$，从而低估了质量损失。对于WASP-33 b，高XUV恒星通量导致质量损失率为$\approx$ 10 $^{11}$ g s $^{-1}$。甚至更高的质量损失率是可能的较小质量的行星轨道EUV明亮的IMS。我们认为，这是微弱的XUV恒星辐射，结合相对较高的行星质量，这限制了行星质量损失率，使KELT-9类系统的长期存在。
Magnetically controlled mass loss from extrasolar planets in close orbits
我们认为磁场的作用，引导和控制质量损失，通过蒸发流出的太阳系外行星，经历紫外线照射。首先，我们提出了分析结果，占行星和恒星磁场，以及从恒星和行星的质量损失。然后，我们进行了一系列的气体巨行星的数值模拟，并改变行星场强度，背景恒星场强度，紫外加热通量，和行星质量。这些模拟表明，对于中等场强甚至最高的UV通量，即，行星表面场$B_P\gtrsim 0.3$高斯和通量$F_{UV}\sim10^{6}$ erg s $^{-1}$。因此，我们的结论是，从所有的热超导体与温和的表面场的外流是磁控。包含磁场高度抑制流出从夜侧的行星。只有磁极附近的磁场线是开放的，并允许流出发生。开放场线的比例敏感地依赖于恒星背景磁场的强度（和几何形状），以及紫外线加热速率。磁场的净效应是将质量损失率抑制（大约）一个数量级。最后，一些开放的场线不允许流动顺利通过音速点;沿这些流线的流动不会达到稳定状态，导致随时间变化的质量损失。
