On the Chemical Abundance of HR 8799 and the Planet c
On the Chemical Abundance of HR 8799 and the Planet c
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关于 HR 8799 和地球 c 的化学丰度
DOI：
10.3847/1538-3881/ababa7
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
J. Stone
中科院分区：
文献类型：
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作者：
J. Wang 王;Jason J. 飞 Wang 王劲;B. Ma;J. Chilcote;S. Ertel;O. Guyon;I. Ilyin;N. Jovanovic;P. Kalas;J. Lozi;B. Macintosh;K. Strassmeier;J. Stone
通过比较行星和主恒星的化学丰度，揭示了行星的起源和形成路径。恒星丰度是用高分辨率光谱学测量的。另一方面，行星丰度通常是从低分辨率数据中推断出来的。对于直接成像的系外行星，数据可以从一系列高对比度成像/光谱分析仪器中获得。在这里，我们研究了HR 8799及其行星c的化学丰度。我们使用LBT/Pepsi(R=120,000)和存档的HARPS数据测量恒星丰度：恒星[C/H]、[O/H]和C/O分别为0.11±0.12、0.12±0.14，均与太阳值一致。我们利用新获得的Subaru/Charis数据以及Gemini/GPI和Keck/OSIRIS的存档数据进行大气反演。我们使用posettRADTRANS对行星光谱进行建模，并使用PyMultiNest进行反演。反演的行星丰度可以按∼0.5Dex变化，从恒星以下到恒星中的C和O丰度。这种差异取决于是否选择了强有力的先例来确保合理的行星质量。此外，与前人的工作相比，也揭示了丰度测量的不一致性。我们讨论了可能导致不一致的潜在问题，例如，单个数据集的系统学以及检索中物理和化学上的不同假设。我们的结论是，除非这些问题得到完全解决，否则不可能获得稳健的检索。
Comparing chemical abundances of a planet and the host star reveals the origin and formation pathway of the planet. Stellar abundance is measured with high-resolution spectroscopy. Planet abundance, on the other hand, is usually inferred from low-resolution data. For directly imaged exoplanets, the data are available from a slew of high-contrast imaging/spectroscopy instruments. Here, we study the chemical abundance of HR 8799 and its planet c. We measure stellar abundance using LBT/PEPSI (R = 120,000) and archival HARPS data: stellar [C/H], [O/H], and C/O are 0.11 ± 0.12, 0.12 ± 0.14, and , all consistent with solar values. We conduct atmospheric retrieval using newly obtained Subaru/CHARIS data together with archival Gemini/GPI and Keck/OSIRIS data. We model the planet spectrum with petitRADTRANS and conduct retrieval using PyMultiNest. Retrieved planetary abundance can vary by ∼0.5 dex, from sub-stellar to stellar C and O abundances. The variation depends on whether strong priors are chosen to ensure a reasonable planet mass. Moreover, comparison with previous works also reveals inconsistency in abundance measurements. We discuss potential issues that can cause the inconsistency, e.g., systematics in individual data sets and different assumptions in the physics and chemistry in retrieval. We conclude that no robust retrieval can be obtained unless the issues are fully resolved.