论文标题
从氢Balmer系列的Kelt-9 B热层的质量损耗率和局部热力学状态
Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series
论文作者
论文摘要
Kelt-9 B，是最热门的外部活动，带有$ t \ sim4400 $ k，是一个被称为超热木星的新星球类的原型。假定这些系外行星的气氛由中性和电离原子物种主导。特别是，在Kelt-9 B上层大气中检测到H $α$和H $β$ Balmer线，这表明氢气填充了行星Roche Lobe，并逃离了行星。在这项工作中，我们检测到$δ$ scuti型恒星脉动（$ p = 7.54 \ pm0.12 $ h），并研究了rossiter-mclaughlin效果（在positial formitial formation（旋转角度$λ= -85.01^°\ pm0.23^°$）之前（在$ pos）上（$ coptial to pm pm0.23^°$）（$ $）$ $ $ $ $） Kelt-9 b。我们的HARPS-N数据显示H $α$对H $δ$的显着吸收。 H $α$，H $β$和H $γ$吸收的精确线形状使我们能够对热层温度施加约束。此外，由于使用新的大气模型进行了检索分析，质量损失率和Kelt-9 B的激发氢数量也受到限制。 We retrieved a thermospheric temperature of $T=13200^{+800}_{-720}$ K and a mass loss rate of $\dot{M}=10^{12.8\pm0.3}$ g s$^{-1}$ when the atmosphere was assumed to be in hydrodynamical expansion and in local thermodynamic equilibrium (LTE).由于预计热木星的热球不会在LTE中，因此我们针对激发氢的种群探索了具有非玻尔兹曼平衡的大气结构。我们没有找到有力的统计证据，而是为了离开LTE离开。但是，我们的非LTE场景表明，与Boltzmann平衡的偏离可能不足以解释激发氢的低数量密度。在非LTE中，SAHA平衡通过光电发化也可能需要解释数据。
KELT-9 b, the hottest known exoplanet with $T\sim4400$ K, is the archetype of a new planet class known as ultra-hot Jupiters. These exoplanets are presumed to have an atmosphere dominated by neutral and ionized atomic species. In particular, H$α$ and H$β$ Balmer lines have been detected in the KELT-9 b upper atmosphere, suggesting that hydrogen is filling the planetary Roche lobe and escaping from the planet. In this work, we detected $δ$ Scuti-type stellar pulsation (with a period $P=7.54\pm0.12$ h) and studied the Rossiter-McLaughlin effect (finding a spin-orbit angle $λ=-85.01^°\pm0.23^°$) prior to focussing on the Balmer lines (H$α$ to H$ζ$) in the optical transmission spectrum of KELT-9 b. Our HARPS-N data show significant absorption for H$α$ to H$δ$. The precise line shapes of the H$α$, H$β$, and H$γ$ absorptions allow us to put constraints on the thermospheric temperature. Moreover, the mass loss rate, and the excited hydrogen population of KELT-9 b are also constrained, thanks to a retrieval analysis performed with a new atmospheric model. We retrieved a thermospheric temperature of $T=13200^{+800}_{-720}$ K and a mass loss rate of $\dot{M}=10^{12.8\pm0.3}$ g s$^{-1}$ when the atmosphere was assumed to be in hydrodynamical expansion and in local thermodynamic equilibrium (LTE). Since the thermospheres of hot Jupiters are not expected to be in LTE, we explored atmospheric structures with non-Boltzmann equilibrium for the population of the excited hydrogen. We do not find strong statistical evidence in favor of a departure from LTE. However, our non-LTE scenario suggests that a departure from the Boltzmann equilibrium may not be sufficient to explain the retrieved low number densities of the excited hydrogen. In non-LTE, Saha equilibrium departure via photo-ionization, is also likely to be necessary to explain the data.
