日冕物质抛射和耀斑对热木星HD189733b大气的影响
The impact of coronal mass ejections and flares on the atmosphere of the hot Jupiter HD189733b
摘要：
高能恒星辐射可以使行星大气光蒸发，这可以在氢线的光谱凌日中观察到。对于系外行星HD 189733 b，在Ly- $α$线上的多次观测表明，大气蒸发是可变的，在$1.5$ -年的间隔内从未检测到的蒸发到增强的蒸发。巧合的是，当HD 189733 b被观测到蒸发时，在观测前8小时刚刚发生了一次恒星耀斑。这就引出了一个问题，即蒸发量的这种时间变化是否是由于耀斑、一次看不见的相关日冕物质抛射（CME），或者甚至是两者同时发生的影响而发生的。在这项工作中，我们调查耀斑（辐射），风和日冕物质抛射（粒子）对HD 189733 b大气的影响，使用三维辐射流体动力学模拟大气蒸发，自洽包括恒星光子加热。我们研究四个案例：第一-恒星的静止阶段，包括恒星风，第二-耀斑，第三-CME，第四-耀斑之后是CME。与静止的情况相比，我们发现，耀斑单独增加的蒸发率只有25%，而CME导致逃逸率增加了4倍。我们计算了Ly- $α$合成凌日，发现耀斑本身不能解释在Ly- $α$观测中观察到的高蓝移速度。然而，日冕物质抛射导致逃逸大气的速度增加，在高蓝移速度下增强了过境深度。虽然CME的影响显示出解释蓝移线特征的潜力，但我们的模型无法完全解释蓝移过境深度，这表明它们可能需要额外的物理机制。
英文摘要：
High-energy stellar irradiation can photoevaporate planetary atmospheres, which can be observed in spectroscopic transits of hydrogen lines. For the exoplanet HD189733b, multiple observations in the Ly-$α$ line have shown that atmospheric evaporation is variable, going from undetected to enhanced evaporation in a $1.5$-year interval. Coincidentally or not, when HD189733b was observed to be evaporating, a stellar flare had just occurred 8h prior to the observation. This led to the question of whether this temporal variation in evaporation occurred due to the flare, an unseen associated coronal mass ejection (CME), or even the effect of both simultaneously. In this work, we investigate the impact of flares (radiation), winds, and CMEs (particles) on the atmosphere of HD189733b using 3D radiation hydrodynamic simulations of atmospheric evaporation that self-consistently include stellar photon heating. We study four cases: first- the quiescent phase of the star including stellar wind, second- a flare, third- a CME, and fourth- a flare that is followed by a CME. Compared to the quiescent case, we find that the flare alone increases the evaporation rate by only 25%, while the CME leads to a factor of 4 increase in escape rate. We calculate Ly-$α$ synthetic transits and find that the flare alone cannot explain the observed high blueshifted velocities seen in the Ly-$α$ observation. The CME, however, leads to an increase in the velocity of the escaping atmosphere, enhancing the transit depth at high blueshifted velocities. While the effects of CMEs show a promising potential to explain the blueshifted line feature, our models are not able to fully explain the blueshifted transit depths, indicating that they might require additional physical mechanisms.
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