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arXiv 2303.09501astro-ph.EP
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关于热木星WASP-80b高层大气中亚稳态HeI未被探测到的起源研究

On the origin of the non-detection of metastable HeI in the upper atmosphere of the hot Jupiter WASP-80b

L. Fossati, I. Pillitteri, I. F. Shaikhislamov, A. Bonfanti, F. Borsa, I. Carleo, G. Guilluy, M. S. Rumenskikh

AI总结:

本研究通过观测数据推导恒星极紫外通量、开展三维磁流体动力学模拟,探究热木星WASP-80b高层大气中亚稳态HeI未被探测到的成因,指出低星冕[Fe/O]丰度导致的低恒星EUV通量是主因,并强调高质量EUV光谱对提升行星大气表征能力的重要性。

摘要:

我们旨在厘清热木星WASP-80b在约10830埃处亚稳态HeI三重线未被探测到的成因。我们从存档观测数据中测量了WASP-80的X射线通量,并将其作为输入代入考虑了星冕[Fe/O]丰度比的标度关系,以推断200-504埃波段的极紫外(EUV)通量,该波段的辐射控制着亚稳态HeI的形成。我们开展了膨胀的行星高层大气与恒星风相互作用的三维(磁)流体动力学模拟,以研究恒星高能辐射、He/H丰度比、恒星风,以及可能存在的强度最高达1G的行星磁场对HeI吸收的影响。对于测得的logR'HK值所支持的低恒星EUV辐射情况,HeI未被探测到的原因可以是太阳型He/H丰度比结合强恒星风,或是低于太阳的He/H丰度比,或是两者的共同作用。对于高恒星EUV辐射的情况,未探测到HeI则意味着行星He/H丰度比低于太阳值。行星磁场不太可能是导致未探测到HeI的原因。由低[Fe/O]星冕丰度导致的低恒星EUV通量,可能是HeI未被探测到的主要原因。目前迫切需要获取近邻恒星的高质量EUV光谱,以提高高能辐射估算的精度,进而能够利用观测结果约束行星He/H丰度比和恒星风强度。这将大幅提升从HeI大气表征观测中可提取的信息量。

英文摘要:

We aim to narrow down the origin of the non-detection of the metastable HeI triplet at about 10830 A obtained for the hot Jupiter WASP-80b. We measure the X-ray flux of WASP-80 from archival observations and use it as input to scaling relations accounting for the coronal [Fe/O] abundance ratio to infer the extreme-ultraviolet (EUV) flux in the 200-504 A range, which controls the formation of metastable HeI. We run three dimensional (magneto) hydrodynamic simulations of the expanding planetary upper atmosphere interacting with the stellar wind to study the impact on the HeI absorption of the stellar high-energy emission, the He/H abundance ratio, the stellar wind, and the possible presence of a planetary magnetic field up to 1 G. For a low stellar EUV emission, which is favoured by the measured logR'HK value, the HeI non-detection can be explained by a solar He/H abundance ratio in combination with a strong stellar wind, or by a sub-solar He/H abundance ratio, or by a combination of the two. For a high stellar EUV emission, the non-detection implies a sub-solar He/H abundance ratio. A planetary magnetic field is unlikely to be the cause of the non-detection. The low EUV stellar flux, driven by the low [Fe/O] coronal abundance, is the likely primary cause of the HeI non-detection. High-quality EUV spectra of nearby stars are urgently needed to improve the accuracy of high-energy emission estimates, which would then enable one to employ the observations to constrain the planetary He/H abundance ratio and the stellar wind strength. This would greatly enhance the information that can be extracted from HeI atmospheric characterisation observations.

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