[论文解读] A second visit to Eps Ind Ab with JWST: new photometry confirms ammonia and suggests thick clouds in the exoplanet atmosphere of the closest super-Jupiter

Elisabeth C. Matthews, James Mang+10 more|arXiv (Cornell University)|Mar 9, 2026

Stellar, planetary, and galactic studies被引用 0

一句话总结

New JWST/MIRI photometry confirms ammonia in Eps Ind Ab and suggests thick water-ice clouds; updated orbit mass is 7.6±0.7 M_Jup with eccentricity ~0.24.

ABSTRACT

With JWST, we are directly imaging cold (~200-300K), solar-age giant exoplanets for the first time. At these temperatures many molecular features appear and water-ice clouds may condense and affect the emission spectrum; early photometric measurements of cold giant planets are already showing some tension with the predictions of cloud-free, solar-metallicity atmosphere models. Here we present new JWST/MIRI coronagraphic observations of the cold giant exoplanet Eps Ind Ab at 11.3um. Together with archival data, we use these new observations to study the atmosphere of this cold exoplanet, and we also re-fit its orbit, finding an updated mass of $7.6\pm0.7$ Mj and an eccentricity of $0.24^{+0.11}_{-0.08}$. The planet is significantly brighter (by $0.88\pm0.08$ mag) at 11.3um than at 10.6um, indicating the presence of ammonia. However, this ammonia feature is shallower than expected. This could indicate a low-metallicity or nitrogen-depleted atmosphere, but our preferred explanation is the presence of thick water-ice clouds that suppress the ammonia feature and the near-IR emission of Eps Ind Ab. Photometry of the small but growing sample of cold, giant exoplanets demonstrates that they are consistently fainter than expected between 3 to 5um, consistent with the water-ice cloud hypothesis. 10.6um and 11.3um photometry of this cold exoplanet sample would be valuable to determine whether the suppressed ammonia feature is universal, and to frame a new open question about the underlying physical cause.

研究动机与目标

• Motivate direct atmospheric characterization of the cold (~275 K) exoplanet Eps Ind Ab.
• Test for ammonia absorption using JWST/MIRI filters F1065C and F1140C.
• Re-fit the orbit to refine mass and eccentricity using new imaging and archival RV data.

提出的方法

• Obtain JWST/MIRI coronagraphic photometry in F1140C with 4QPM and collect background/PSF reference data for PSF subtraction.
• Reduce data with spaceKLIP/RDI to model and subtract stellar PSF and extract companion photometry across multiple methods.
• Compute photometry with three independent approaches (spaceKLIP companion injection, STPSF-based PSF modeling, and TA contrast relative to host star) to derive robust fluxes and colors.
• Combine new and archival photometry to assess ammonia presence via F1065C−F1140C color (ammonia opacity) and compare to atmospheric models.
• Use CMDs and Sonora Flame Skimmer models to interpret atmospheric parameters (metallicity, C/O, clouds, and Kzz) and to explore nitrogen depletion scenarios.
• Self-consistently test the impact of thick water-ice clouds on the observed photometry using PICASO/Virga cloud models.

Figure 1: Coronagraphic images of Eps Ind A, collected with the F1140C filter of JWST/MIRI. The planet is detected as a bright point source in upper left of this image.

实验结果

研究问题

• RQ1 Eps Ind Ab的大气中是否存在氨分子，并能通过 F1065C 与 F1140C 的 JWST/MIRI 过滤器检出？
• RQ2 近I_r 3–5 µm 与中红外颜色对 Eps Ind Ab 的金属丰度、C/O 比及云特性（尤其是水冰云）有何指示？
• RQ3 更新的天体测量和径向速度数据是否能更精确地约束 Eps Ind Ab 的动力学质量与轨道？
• RQ4 氮的耗减或云过程是否会抑制在最冷的外行星大气中的氨特征，且此现象是否在相似对象中普遍存在？

主要发现

Filter	Adopted Flux (arbitrary units)	Apparent Magnitude [mag]	Absolute Magnitude [mag]	Notes
F1065C	5.09 ± 0.12	13.13 ± 0.03	15.33 ± 0.03	Adopted from spaceKLIP method; photometry used to derive colors
F1140C	9.08 ± 0.64	12.21 ± 0.08	14.40 ± 0.08	Adopted from TA/contrast method; higher uncertainty acknowledged
F1550C	6.80 ± 0.52	11.16 ± 0.08	13.36 ± 0.08	Adopted from spaceKLIP method; color used for CMDs

• F1065C−F1140C 颜色为 0.88±0.08 mag，指示显著的氨特征，但比无云太阳金属丰度预测的强度要浅。
• 大气模型倾向于厚水冰云、较高的金属丰度与 C/O，以再现观测到的光度并抑制氨深度，与在3–5 µm处的非探测结果一致。
• 相比 CMD 分析显示 Eps Ind Ab 与极冷的 WISE 0855 具有相似的中红外颜色，暗示在冷态区有共同的浅氨行为。
• 氮耗减（约等于平衡 NH3 丰度的5–15%）结合高金属丰度和 C/O 可匹配 F1065C−F1140C 颜色与近红外约束，尽管云/云相互作用情景仍被看好。
• 与恒星的共同运动性被确认，更新的轨道拟合给出动力学质量为 7.6±0.7 M_Jup，偏心率为 0.24^{+0.11}_{-0.08}。

Figure 2: Opacity of ammonia as a function of wavelength (left axis), plotted against the transmission of the MIRI coronagraphic filters (right axis). The deep, double-peaked 10-11µm ammonia absorption feature falls primariy in the F1065C filter, and the F1065C-F1140C color is a proxy for the depth