[论文解读] Time-resolved transmission spectroscopy of the ultra-hot Jupiter WASP-189 b

Bibiana Prinoth, H. J. Hoeijmakers+15 more|arXiv (Cornell University)|Aug 8, 2023

Astro and Planetary Science被引用 1

一句话总结

本研究利用HARPS、HARPS-N、ESPRESSO和MAROON-X在八次凌日观测中对超热木星WASP-189 b进行了时间分辨的高分辨率透射光谱观测。首次在该行星大气中探测到Sr、Sr+和Ba+，并通过多仪器后续观测确认了TiO的存在，揭示了与大气动力学及晨昏线区域热不均匀性相关的信号不对称性。

ABSTRACT

Ultra-hot Jupiters are tidally locked with their host stars dividing their atmospheres into a hot dayside and a colder nightside. As the planet moves through transit, different regions of the atmosphere rotate into view revealing different chemical regimes. High-resolution spectrographs can observe asymmetries and velocity shifts, and offer the possibility for time-resolved spectroscopy. In this study, we search for other atoms and molecules in the planet`s transmission spectrum and investigate asymmetric signals. We analyse and combine eight transits of the ultra-hot Jupiter WASP-189 b taken with the HARPS, HARPS-N, ESPRESSO and MAROON-X high-resolution spectrographs. Using the cross-correlation technique, we search for neutral and ionised atoms, and oxides and compare the obtained signals to model predictions. We report significant detections for H, Na, Mg, Ca, Ca+, Ti, Ti+, TiO, V, Cr, Mn, Fe, Fe+, Ni, Sr, Sr+, and Ba+. Of these, Sr, Sr+, and Ba+ are detected for the first time in the transmission spectrum of WASP-189 b. In addition, we robustly confirm the detection of titanium oxide based on observations with HARPS and HARPS-N using the follow-up observations performed with MAROON-X and ESPRESSO. By fitting the orbital traces of the detected species by means of time-resolved spectroscopy using a Bayesian framework, we infer posterior distributions for orbital parameters as well as lineshapes. Our results indicate that different species must originate from different regions of the atmosphere to be able to explain the observed time dependence of the signals. Throughout the course of the transit, most signal strengths are expected to increase due to the larger atmospheric scale height at the hotter trailing terminator. For some species, however, the signals are instead observed to weaken due to ionisation for atoms and their ions, or the dissociation of molecules on the dayside.

研究动机与目标

• 利用高分辨率光谱研究超热木星WASP-189 b的大气化学不均性和动力学特征。
• 在已知物种之外，探测行星透射光谱中新的原子和分子物种。
• 分析随时间变化的光谱信号，以推断大气结构及探测物种的起源区域。
• 通过多仪器后续观测验证并确认先前对TiO的探测结果。
• 使用贝叶斯框架对轨道速度位移和谱线形状进行建模，以约束大气特性。

提出的方法

• 结合使用高分辨率光谱仪HARPS、HARPS-N、ESPRESSO和MAROON-X对WASP-189 b的八次凌日事件进行观测。
• 应用互相关技术在透射光谱中探测中性原子、离子物种及氧化物。
• 采用贝叶斯框架拟合轨道轨迹，推断轨道参数和谱线形状的后验分布。
• 将观测信号与模型预测进行比较，以评估探测显著性及物理一致性。
• 在后验分布达到先验边界时，强制要求轨道速度在不同凌日相位保持一致。
• 分析凌日过程中信号的演化，以推断大气标高及离子化、解离等化学过程。

实验结果

研究问题

• RQ1 利用高分辨率光谱技术，能否在WASP-189 b的透射光谱中探测到新的原子和分子物种？
• RQ2 探测物种的时间依赖性信号如何随凌日过程变化？这些信号揭示了哪些关于大气结构的信息？
• RQ3 哪些物理过程（如离子化、解离、热膨胀）可解释观测到的信号不对称性？
• RQ4 能否通过多台仪器的后续观测可靠地确认TiO的探测结果？
• RQ5 不同物种是否源自不同的大气区域，例如白天一侧或晨昏线区域？

主要发现

• 本研究报告了H、Na、Mg、Ca、Ca+、Ti、Ti+、TiO、V、Cr、Mn、Fe、Fe+、Ni、Sr、Sr+和Ba+的显著探测结果，其中Sr、Sr+和Ba+为首次在WASP-189 b大气中探测到。
• Sr、Sr+和Ba+的探测显著性超过10σ，表明其探测结果具有高度稳健性和可靠性。
• 通过MAROON-X和ESPRESSO的后续观测，对TiO的探测结果得到稳健确认，支持了此前HARPS和HARPS-N的发现。
• 大多数物种的信号强度在凌日过程中增强，这与较热的后方晨昏线区域大气标高增加有关。
• 对于部分物种（如Fe+和Ti+），观察到信号减弱，可能源于白天一侧的离子化或解离过程。
• 时间分辨建模表明，不同物种源自不同的大气区域，其谱线形状和速度位移在凌日过程中表现出显著差异。