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arXiv 2001.06430astro-ph.EP
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超热木星WASP-121 b大气中Fe I的探测和多普勒分辨光谱学的新的基于似然的方法

Detection of Fe I in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy

Neale P. Gibson, Stephanie Merritt, Stevanus K. Nugroho, Patricio E. Cubillos, Ernst J. W. de Mooij, Thomas Mikal-Evans, Luca Fossati, Joshua Lothringer, Nikola… 展开作者

Neale P. Gibson, Stephanie Merritt, Stevanus K. Nugroho, Patricio E. Cubillos, Ernst J. W. de Mooij, Thomas Mikal-Evans, Luca Fossati, Joshua Lothringer, Nikolay Nikolov, David K. Sing, Jessica J. Spake, Chris A. Watson, Jamie Wilson

摘要:

高分辨率多普勒分辨光谱学为研究过境和非过境系外行星的大气层开辟了一个新的窗口。在这里,我们提出了VLT/UVES观测的过境WASP-121 b,一个“超热”木星先前发现表现出温度反演和检测的多个物种在光学波长。我们目前的初步结果使用UVES($\approx$ 3700- 5000 A)的蓝臂,恢复了明确的信号中性铁在行星的大气中在>8 $σ$,这可能有助于(甚至完全解释)在平流层的逆温。然而,使用标准的互相关方法,很难提取物理参数,如温度和丰度。最近的开拓性努力试图开发可能性“映射”,可用于直接拟合模型到高分辨率数据集。我们引入了一个新的框架,直接计算模型拟合数据的可能性,并可用于通过MCMC技术探索参数化模型大气的后验分布。我们的方法还恢复了大气的物理范围,以及占时间和波长相关的不确定性。我们测量的温度为$3710^{+490}_{-510}$ K,这表明与低分辨率观测相比,高层大气的温度更高。我们还表明,Fe I信号是物理分离的外大气Fe II。然而,温度测量与气溶胶性质高度退化;使用更复杂的大气模型检测其他物种,或将这些方法与低分辨率光谱相结合,应有助于打破这些退化。

英文摘要:

High-resolution Doppler-resolved spectroscopy has opened up a new window into the atmospheres of both transiting and non-transiting exoplanets. Here, we present VLT/UVES observations of a transit of WASP-121b, an 'ultra-hot' Jupiter previously found to exhibit a temperature inversion and detections of multiple species at optical wavelengths. We present initial results using the blue arm of UVES ($\approx$3700-5000A), recovering a clear signal of neutral Fe in the planet's atmosphere at >8$σ$, which could contribute to (or even fully explain) the temperature inversion in the stratosphere. However, using standard cross-correlation methods, it is difficult to extract physical parameters such as temperature and abundances. Recent pioneering efforts have sought to develop likelihood `mappings' that can be used to directly fit models to high-resolution datasets. We introduce a new framework that directly computes the likelihood of the model fit to the data, and can be used to explore the posterior distribution of parameterised model atmospheres via MCMC techniques. Our method also recovers the physical extent of the atmosphere, as well as account for time- and wavelength-dependent uncertainties. We measure a temperature of $3710^{+490}_{-510}$K, indicating a higher temperature in the upper atmosphere when compared to low-resolution observations. We also show that the Fe I signal is physically separated from the exospheric Fe II. However, the temperature measurements are highly degenerate with aerosol properties; detection of additional species, using more sophisticated atmospheric models, or combining these methods with low-resolution spectra should help break these degeneracies.

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