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arXiv 2202.02041astro-ph.EP
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在超热彗星中寻找Escherichreich效应的起源:WASP-76 b大气中强C/O梯度的证据?

Searching for the origin of the Ehrenreich effect in ultra-hot Jupiters: Evidence for strong C/O gradients in the atmosphere of WASP-76b?

A. Sánchez-López, R. Landman, P. Mollière, N. Casasayas-Barris, A. Y. Kesseli, I. A. G. Snellen

摘要:

极热彗星的昼夜极端温度差异导致了显著不对称的大气层,在终结者周围的小范围经度上发生了巨大的膨胀。在凌日过程中,WASP-76 b旋转约30度,改变了大气的可观测部分,并引起其成分外观的变化。正如最近报道的那样,这导致了中性铁信号的时变效应,而中性铁信号可能在夜面凝结而被放大。在这里,我们研究了在与CARMENES摄谱仪观察到的WASP-76 b过境期间分子信号的存在,并比较了这颗行星的早晨和晚上终结者的贡献。结果有些令人困惑,正式检测到水蒸气(5.5 $σ$)和氰化氢(5.2 $σ$),但在K $_p$ -V $_{sys}$图中的位置明显不同,蓝移为-14.3 $\pm$ 2.6 km/s,红移为$+$ 20.8 $^{+7.8}_{-3.9}$ km/s,K $_p$高于预期。H $_2$ O的信号也出现较强的过境后,相比之下,HCN,这似乎更强的早期。我们尝试解释这硅酸盐云的形成和下雨的夜面,部分从高层大气中除去氧气。对于C/O值在0.7和1之间,这导致HCN在晨肢形成。在傍晚终止时,由于蒸发,隔离的氧返回气相,这些C/O值导致形成H $_2$ O而不是HCN。如果得到证实,这些结果表明,单个分子跟踪大气的不同部分,以及夜面凝结,允许空间表征。由于这些结果是基于一个单一的过境,我们主张需要更多的数据来确认它们,并进一步探讨这些情况。

英文摘要:

Extreme temperature contrasts between the day and nightside of ultra-hot Jupiters result in significantly asymmetric atmospheres, with a large expansion occurring over a small range of longitude around the terminator. Over the course of a transit, WASP-76b rotates by about 30 degree, changing the observable part of the atmosphere and invoking variations in the appearance of its constituents. As recently reported, this results in time-variable effects in the neutral iron signal, which are amplified by its possible condensation on the nightside. Here, we study the presence of molecular signals during a transit of WASP-76b observed with the CARMENES spectrograph and compare the contributions from this planet's morning and evening terminators. The results are somewhat puzzling, with formal detections of water vapor (5.5$σ$) and hydrogen cyanide (5.2$σ$) but at significantly different positions in the K$_p$-V$_{sys}$ diagram, with a blueshift of -14.3 $\pm$ 2.6 km/s and a redshift of $+$20.8 $^{+7.8}_{-3.9}$ km/s respectively, and a higher K$_p$ than expected. The H$_2$O signal also appears stronger later on in the transit, in contrast to that of HCN, which seems stronger early on. We tentatively explain this by silicate clouds forming and raining out on the nightside, partially removing oxygen from the upper atmosphere. For C/O values between 0.7 and 1, this leads to the formation of HCN at the morning limb. At the evening terminator, with the sequestered oxygen being returned to the gas phase due to evaporation, these C/O values lead to formation of H$_2$O instead of HCN. If confirmed, these results indicate that individual molecules trace different parts of the atmosphere, as well as nightside condensation, allowing spatial characterization. As these results are based on a single transit, we advocate that more data are needed to confirm them and further explore these scenarios.

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