[论文解读] The ESO SupJup Survey IX: Isotopic evidence of a recent formation for Luhman 16AB

S. de Regt, I. A. G. Snellen+9 more|arXiv (Cornell University)|Feb 3, 2026

Stellar, planetary, and galactic studies被引用 0

一句话总结

论文利用高分辨率的K波段检索对Luhman 16A和B进行元素与同位素丰度测定，发现近太阳C/O、金属性增强、以及相同的12C/13C比，支持它们在Oceanus移动群内具有共同且相对年轻的形成历史。

ABSTRACT

The distinct formation pathways of directly-imaged exoplanets and isolated brown dwarfs might leave imprints in the inherited elemental and isotopic abundances, but such measurements require careful characterisation of the atmospheres. In particular, L-T transition objects exhibit signs of dynamics that drive their atmospheres out of chemical equilibrium. In this work, we studied the nearest L-T brown dwarfs, Luhman 16A and B, to assess the chemical dis-equilibrium in their atmospheres and to investigate their elemental and isotopic composition. As part of the ESO SupJup Survey, we obtained high-resolution CRIRES$^+$ K-band spectra of the binary, which were analysed using an atmospheric retrieval framework. We detect and retrieve the abundances of $^{12}$CO, H$_2$O, CH$_4$, NH$_3$, H$_2$S, HF, and the $^{13}$CO isotopologue. Both atmospheres are in chemical dis-equilibrium with somewhat stronger vertical mixing in Luhman 16A compared to B ($K_\mathrm{zz,A}\sim10^{8.7}$, $K_\mathrm{zz,B}\sim10^{8.2}\ \mathrm{cm^2\ s^{-1}}$). The tested chemical models, free- and dis-equilibrium chemistry, yield consistent mixing ratios and agree with earlier work at shorter wavelengths. The gaseous C/O ratios show evidence of oxygen trapping in silicate-oxide clouds. While the C/O ratios are consistent with solar, the metallicities are modestly enhanced with $\mathrm{[C/H]}\sim0.15$. The carbon isotope ratios are measured at $\mathrm{^{12}C/^{13}C_A}=74^{+2}_{-2}$ and $\mathrm{^{12}C/^{13}C_B}=74^{+3}_{-3}$. The coincident constraints of metallicities and isotopes across the binary reinforce their likely shared formation. The $\mathrm{^{12}C/^{13}C}$ ratios are aligned with the present-day interstellar medium, but lower than the solar-system value. This suggests a recent inheritance and corroborates the relatively young age ($\sim500$ Myr) of Luhman 16AB as members of the Oceanus moving group.

研究动机与目标

• 评估最近的Luhman 16A和B大气中的化学非平衡。
• 限制元素丰度与同位素比，以了解形成历史。
• 检验自由化学与非平衡化学模型在大气组成上的一致性。
• 通过比较金属性与同位素比，评估双星成分是否具有共同起源。

提出的方法

• 取得Luhman 16A与B在R~60,000分辨率下的空间分辨CRIES+ K波段光谱。
• 使用耦合petitRADTRANS的PyMultiNest取样的大气检索框架。
• 比较自由化学与非平衡化学模型以推导VMR与元素丰度。
• 检索13CO、C18O、C17O、H2-18O、H2-17O同位素同分子丰度并约束C/O与[X/H]。
• 计算淬火压力和垂直混合产生的Kzz，以评估非平衡。
• 将丰度投射到固定的log g值以确保跨分量的一致性。

Figure 1 : CRIRES + K-band spectra of Luhman 16A and B in orange and blue, respectively. Top panel : Seven spectral orders covered in the K2166 wavelength setting. The telluric absorption is shown as transparent lines. Lower panels : Zoom-in of the sixth order. The black observed spectra are overlai

实验结果

研究问题

• RQ1 从高分辨率K波段光谱中，Luhman 16A和B的元素与同位素组成是什么？
• RQ2 C/O比与12C/13C同位素比是否支持二元星在Oceanus移动群内具有共同的形成历史？
• RQ3 两者之间的化学非平衡（垂直混合）有何差异，对大气化学有何影响？
• RQ4 金属性与C/O比是否符合太阳组成，或相对于太阳显示出增强的金属性？
• RQ5 同位素测量是否与当前星际介质值相吻合，暗示来自原始云的最近继承？

主要发现

• 两者均表现出化学非平衡且垂直混合显著，A的Kzz约为10^8.7 cm^2 s^-1，B为约10^8.2 cm^2 s^-1。
• 测得的12C/13C比为A为74（+2/-2），B为74（+3/-3），与局部ISМ相符但低于太阳值。
• 自由化学C/O≈0.651（+0.002/-0.002）为A，≈0.646（+0.002/-0.002）为B；而非平衡/整体C/O值较低（A: 0.613(+0.002/-0.002)，B: 0.572(+0.004/-0.003)）。
• 两者均显示适度的超太阳金属性[C/H]≈0.15，且在各模型与双星间一致。
• 在云状硅酸盐氧化物中，氧被“核聚”至固体形态，包含凝结种类时会影响总体C/O。
• A与B在同位素和金属性约束方面相似，支持在Oceanus移动群中的共同、相对年轻的形成方案（约500 Myr）。

Figure 2 : Cross-correlation analysis of minor species in the spectra of Luhman 16A (solid) and B (dashed). The detection significance at $\textit{v}=0\ \mathrm{km\ s^{-1}}$ is indicated in the upper-right corner of each panel, with Luhman 16A at the top. The panel rows use different y-axis limits f