确定热木星HD209458b终止点的大气条件
Determining atmospheric conditions at the terminator of the hot-Jupiter HD209458b
摘要：
我们提出了一个理论模型，适用于HD209458 b的HST/STIS光学渡越透射谱。在我们的拟合中，我们使用钠吸收线轮廓以及H_2的瑞利散射来帮助确定行星终结点的平均温度-压力轮廓，并推断原子和分子物种的丰度。观测到的钠谱线分布跨越约3，500 km的高度范围，对应于我们的大气模型中约0.001和50 mbar之间的压力。我们发现，钠线轮廓需要要么冷凝成硫化钠或电离，必要的消耗原子钠只有在高海拔低于3毫巴的压力。观测到的钠丰度突然变化支持了钠的消耗，从低层大气中的2倍太阳丰度到高层大气中的0.2倍太阳丰度或更低。我们的研究结果还表明，在平流层高度附近存在一个热大气，对应于33毫巴的压力，与所观察到的昼侧温度反演一致。此外，我们发现一个单独的更高的海拔温度上升是必要的冷凝和电离模型，对应的压力低于~0.01毫巴。这种高海拔的高温表明，钠原子的吸收可能会探测到热层的底部，并且可能对与大气逃逸有关的温度上升很敏感。
英文摘要：
We present a theoretical model fit to the HST/STIS optical transit transmission spectrum of HD209458b. In our fit, we use the sodium absorption line profile along with the Rayleigh scattering by H_2 to help determine the average temperature-pressure profile at the planetary terminator, and infer the abundances of atomic and molecular species. The observed sodium line profile spans an altitude range of ~3,500 km, corresponding to pressures between ~0.001 and 50 mbar in our atmospheric models. We find that the sodium line profile requires either condensation into sodium sulfide or ionization, necessary to deplete atomic sodium only at high altitudes below pressures of ~3 mbar. The depletion of sodium is supported by an observed sudden abundance change, from 2 times solar abundance in the lower atmosphere to 0.2 solar or lower in the upper atmosphere. Our findings also indicate the presence of a hot atmosphere near stratospheric altitudes corresponding to pressures of 33 mbar, consistent with that of the observed dayside temperature inversion. In addition, we find a separate higher altitude temperature rise is necessary within both the condensation and ionization models, corresponding to pressures below ~0.01 mbar. This hot higher altitude temperature indicates that absorption by atomic sodium can potentially probe the bottom of the thermosphere, and is possibly sensitive to the temperature rise linked to atmospheric escape.
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