arXiv 2003.048722020-03-12astro-ph.EPastro-ph.SR

模拟HD 209458 b大气中He I在10830埃处的三重吸收

Modelling the He I triplet absorption at 10830 Angstroms in the atmosphere of HD 209458 b

M. Lampón, M. López-Puertas, L. M. Lara, A. Sánchez-López, M. Salz, S. Czesla, J. Sanz-Forcada, K. Molaverdikhani, F. J. Alonso-Floriano, L. Nortmann, J. A. Cab… 展开作者

M. Lampón, M. López-Puertas, L. M. Lara, A. Sánchez-López, M. Salz, S. Czesla, J. Sanz-Forcada, K. Molaverdikhani, F. J. Alonso-Floriano, L. Nortmann, J. A. Caballero, F. F. Bauer, E. Pallé, D. Montes, A. Quirrenbach, E. Nagel, I. Ribas, A. Reiners, P. J. Amado

备注：: Accepted to A&A. 15 Pages, 15 figures and 3 tables
发表信息：: A&A 636, A13 (2020)
DOI：: 10.1051/0004-6361/201937175

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摘要：

HD 209458 b是一颗系外行星，其上层大气正在经历吹离逃逸，主要是通过测量Ly-alpha吸收来研究的。最近，高分辨率测量的吸收在10830埃的几个系外行星（包括HD 209458 b）的He I三重线已被报道，创造了一个新的机会，探测逃逸的大气。我们的目标是更好地了解HD 209458 b的大气区域，即逃逸的起源地。我们开发了一个一维流体动力学模型与球对称的HD 209458 b热层耦合的非本地热力学模型的人口的He三重态。此外，我们进行了高分辨率的辐射转移计算的合成光谱的He三重线，并将它们与测量的吸收光谱，以检索有关的大气参数的信息。我们发现，测量的光谱将[H]/[H $^{+}$ ]跃迁高度限制在1.2 ~ 1.9Rp范围内。H在2.9Rp以上的高度几乎完全电离。我们还发现X射线和极紫外吸收发生在有效半径1.16 - 1.30Rp之间，He三重态密度峰值出现在高度1.04 - 1.60Rp之间。此外，平均毫米波被限制在0.61-0.73克/摩尔区间，热层氢/氦比应大于90/10，最有可能约为98/2。我们还提供了一个一对一的质量损失率和温度之间的关系。基于能量限制逃逸方法，假设加热效率为0.1-0.2，我们得到了质量损失率为（0.42-1.00）$\times 10^{11}$ g/s，相应的温度范围为7125 - 8125 K。对测得的He三重态吸收光谱的分析，大大限制了HD 209458 b的热层结构，并推进了我们对其逃逸大气的认识。

英文摘要：

HD 209458b is an exoplanet with an upper atmosphere undergoing blow-off escape that has mainly been studied using measurements of the Ly-alpha absorption. Recently, high-resolution measurements of absorption in the He I triplet line at 10830 angstroms of several exoplanets (including HD 209458b) have been reported, creating a new opportunity to probe escaping atmospheres. We aim to better understand the atmospheric regions of HD 209458b from where the escape originates. We developed a 1D hydrodynamic model with spherical symmetry for the HD 209458 b thermosphere coupled with a non-local thermodynamic model for the population of the He triplet state. In addition, we performed high-resolution radiative transfer calculations of synthetic spectra for the He triplet lines and compared them with the measured absorption spectrum in order to retrieve information about the atmospheric parameters. We find that the measured spectrum constrains the [H]/[H$^{+}$] transition altitude occurring in the range of 1.2 to 1.9Rp. H is almost fully ionised at altitudes above 2.9Rp. We also find that the X-ray and EUV absorption takes place at effective radii from 1.16 to 1.30Rp, and that the He triplet peak density occurs at altitudes from 1.04 to 1.60Rp. Additionally, the averaged mmw is confined to the 0.61-0.73 g/mole interval, and the thermospheric H/He ratio should be larger than 90/10, and most likely approximately 98/2. We also provide a one-to-one relationship between mass-loss rate and temperature. Based on the energy-limited escape approach and assuming heating efficiencies of 0.1-0.2, we find a mass-loss rate in the range of (0.42-1.00)$\times 10^{11}$ g/s and a corresponding temperature range of 7125 to 8125K. The analysis of the measured He triplet absorption spectrum significantly constrains the thermospheric structure of HD 209458b and advances our knowledge of its escaping atmosphere.

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