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arXiv 2402.09533astro-ph.EPastro-ph.SR
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基于低分辨率和高分辨率光谱的年轻巨行星 ROXs 42B b 的大气反演

Atmospheric Retrievals of the Young Giant Planet ROXs 42B b from Low- and High-Resolution Spectroscopy

Julie Inglis, Nicole L. Wallack, Jerry W. Xuan, Heather A. Knutson, Yayaati Chachan, Marta L. Bryan, Brendan P. Bowler, Aishwarya Iyer, Tiffany Kataria, Björn Benneke

AI总结:

本研究结合低高分辨率光谱对年轻巨行星 ROXs 42B b 进行大气反演,发现高分辨率光谱能避免云层导致的参数简并,可靠测定其大气组成。

摘要:

此前已有研究尝试在低分辨率(R~10s-100s)下表征直接成像行星的大气,但云层的存在往往导致反演得到的大气丰度与云层不透明度和温度结构之间产生简并性,从而使反演的组成成分产生偏差。在本研究中,我们对超年轻($\lesssim$ 5 Myr)直接成像行星 ROXs 42B b 进行了反演,使用了来自 Gemini/NIFS 和 Keck/OSIRIS 的降采样低分辨率 $JHK$ 波段光谱,以及来自升级前 Keck/NIRSPAO 的高分辨率 $K$ 波段光谱。使用 petitRADTRANS 的大气反演框架,我们分别分析了这两个数据集,并将两者结合进行了分析。我们还使用 SPHINX 模型网格拟合了宿主恒星(一个年轻的 M 光谱型双星)的恒星丰度及其他物理性质。我们发现,从高分辨率光谱中测得的 ROXs 42B b 的 C/O($0.50\pm0.05$)和金属丰度([Fe/H] = $-0.67\pm0.35$)与其宿主恒星在 1$\sigma$ 范围内一致。从高分辨率光谱反演得到的参数也独立于我们对云模型的选择。相比之下,从低分辨率光谱反演得到的参数在云层与反演的金属丰度和温度结构之间表现出强烈的简并性。当我们同时对两个数据集进行反演时,发现这些简并性有所降低但并未消除,最终结果仍然对云建模的选择高度敏感。我们得出结论,高分辨率光谱为可靠地确定直接成像伴星的大气组成提供了最有希望的途径,且独立于其云层性质。

英文摘要:

Previous attempts have been made to characterize the atmospheres of directly imaged planets at low-resolution (R$\sim$10s-100s), but the presence of clouds has often led to degeneracies in the retrieved atmospheric abundances with cloud opacity and temperature structure that bias retrieved compositions. In this study, we perform retrievals on the ultra-young ($\lesssim$ 5 Myr) directly imaged planet ROXs 42B b with both a downsampled low-resolution $JHK$-band spectrum from Gemini/NIFS and Keck/OSIRIS, and a high-resolution $K$-band spectrum from pre-upgrade Keck/NIRSPAO. Using the atmospheric retrieval framework of petitRADTRANS, we analyze both data sets individually and combined. We additionally fit for the stellar abundances and other physical properties of the host stars, a young M spectral type binary, using the SPHINX model grid. We find that the measured C/O, $0.50\pm0.05$, and metallicity, [Fe/H] = $-0.67\pm0.35$, for ROXs 42B b from our high-resolution spectrum agree with that of its host stars within 1$σ$. The retrieved parameters from the high-resolution spectrum are also independent of our choice of cloud model. In contrast, the retrieved parameters from the low-resolution spectrum show strong degeneracies between the clouds and the retrieved metallicity and temperature structure. When we retrieve on both data sets together, we find that these degeneracies are reduced but not eliminated, and the final results remain highly sensitive to cloud modeling choices. We conclude that high-resolution spectroscopy offers the most promising path for reliably determining atmospheric compositions of directly imaged companions independent of their cloud properties.

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