发表机构
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences; School of Astronomy and Space Sciences, University of Chinese Academy of Sciences; Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（中国科学院国家天文台光学天文重点实验室; 中国科学院大学天文与空间科学学院; 北京师范大学天文与前沿科学研究中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用JWST光谱在三颗基准早型L型矮星中发现气态SiO证据，结合大气反演揭示其硅酸盐云形成机制，为研究L型矮星大气演化提供了关键观测约束。
AI 中文摘要
追踪硅从气态SiO到硅酸盐凝聚的过程，可直接观测L型矮星大气中硅酸盐云的形成过程。本研究利用JWST/NIRSpec与MIRI光谱仪，在HD 89744B、GJ 1048B和LSPM J0632+5053B三颗基准早型L型矮星中发现了气态SiO的证据。通过在多种云模型下进行含与不含SiO的大气反演，确认最强的SiO特征位于4.0-4.2μm和7.7-8.2μm波段，局部似然诊断达到4.6σ。在物理云反演中，8μm波段探测到的压力低于4μm泛音波段，到达平衡态SiO因硅酸盐凝聚而更强烈耗尽的大气层。三颗天体还在数巴压力下显示出致密的Fe不透明度，其推断的气相C/O比与考虑难熔氧封存后的主星成分预期一致。在采用的无定形硅酸盐颗粒Mie处理框架下，硅酸盐矿物学分析表明HD 89744B倾向于Mg₂SiO₄，GJ 1048B则为Mg₂SiO₄与MgSiO₃的混合云。将该框架扩展到更冷的L型矮星，可追踪沿L型矮星序列气态SiO耗尽与硅酸盐云形成的耦合演化。
英文摘要
Tracing silicon from gaseous SiO into silicate condensates provides a direct view of the condensation process that forms silicate clouds in L-dwarf atmospheres. Here we present evidence for gaseous SiO in three benchmark early-L dwarfs, HD 89744B, GJ 1048B, and LSPM J0632+5053B, using JWST/NIRSpec and MIRI spectroscopy. Atmospheric retrievals with and without SiO under multiple cloud prescriptions identify the strongest SiO signatures at 4.0--4.2 and 7.7--8.2 $μ$m, with the local likelihood diagnostic reaching $4.6σ$. In the physical cloud retrievals, the 8 $μ$m band probes lower pressures than the 4 $μ$m overtone, reaching atmospheric layers where equilibrium SiO is more strongly depleted by silicate condensation. All three objects also show compact Fe opacity at pressures of a few bar. Their inferred gas-phase C/O ratios are consistent with expectations from the host-star compositions after accounting for refractory oxygen sequestration. Within the adopted Mie treatment of amorphous silicate grains, the silicate mineralogies favor Mg$_2$SiO$_4$ for HD 89744B and a mixed Mg$_2$SiO$_4$+MgSiO$_3$ cloud for GJ 1048B. Extending this framework to cooler L dwarfs will trace the coupled evolution of gaseous SiO depletion and silicate-cloud formation along the L-dwarf sequence.
Comments17 pages, 4 figures. Submitted to ApJ, comments are welcome
