发表机构
Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale; School of Physics and Astronomy, Sun Yat-sen University; Kavli Institute for Astronomy and Astrophysics, Peking University; Department of Astronomy, Peking University; INAF – Osservatorio Astronomico di Capodimonte; Leiden Observatory, Leiden University; Max-Planck-Institut für Extraterrestrische Physik; Max-Planck-Institut für Astronomie; Earth and Planets Laboratory, Carnegie Institution for Science; Dept. of Astrophysics, University of Vienna; ETH Zürich, Institute for Particle Physics and Astrophysics; Kapteyn Astronomical Institute, Rijksuniversiteit Groningen; Department of Astronomy, University of Michigan（巴黎萨克雷大学，法国国家科学研究中心，空间天体物理研究所; 中山大学物理与天文学院; 北京大学科维理天文与天体物理研究所; 北京大学天文系; 意大利国家天体物理研究所卡波迪蒙特天文台; 莱顿大学莱顿天文台; 马克斯·普朗克地外物理学研究所; 马克斯·普朗克天文学研究所; 卡内基科学学会地球与行星实验室; 维也纳大学天体物理系; 苏黎世联邦理工学院粒子物理与天体物理研究所; 格罗宁根大学卡普坦天文研究所; 密歇根大学天文系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过JWST两历元观测发现极低质量恒星J1605的盘CO发射随吸积率下降而减弱，支持极低质量恒星是T-Tauri恒星缩小版的观点。
AI 中文摘要
研究极低质量恒星（$M_\star<0.2M_\odot$）的原行星盘结构对于理解类地行星的形成至关重要。本文通过分析2024年获取的新的JWST/NIRSpec观测数据，对已知极低质量恒星2MASS J16053215-1933159（以下简称J1605）周围盘的最内层区域进行了表征，这些观测是在首次使用JWST/MIRI观测两年后进行的。我们发现，在两个观测历元（2022年和2024年）之间，CO通量减少了约3倍，NIRSpec和MIRI均观测到的HI 10-6谱线通量减少了约13倍，总连续谱密度通量减少了约15%。由各HI谱线推导出的吸积率与两年内约13倍的下降幅度一致。在从J1605恒星光球层中存在的CO吸收校正光谱后，我们发现盘的CO发射减少与每个历元具有相同柱密度和温度的CO气体一致，但在吸积率较低时，发射区域面积更小。虽然使用MIRI-MRS检测到了暖烃类（约500 K），且C2H2柱密度极高，但NIRSpec未观测到任何烃类特征。我们提出非局部热动平衡效应抑制了暖储库中烃类的近红外发射。J1605的吸积光度变化与其基频CO光度变化的相关性方式与T-Tauri恒星类似，支持了极低质量恒星可被视为T-Tauri恒星缩小版的观点。在冷天体周围的盘中探测基频CO带发射具有挑战性，因为其光球层中存在CO吸收。未来的观测（例如使用ELT/METIS）若寻找此类发射，将需要稳健的方法来约束光球层发射。
英文摘要
Studying the structure of very-low-mass stars ($M_\star<0.2M_\odot$) protoplanetary disk is crucial to understand the formation of Earth-like planets. In this paper, we characterize the innermost regions of the disk around a known very-low-mass star, 2MASS J16053215-1933159 (J1605 hereafter), by analyzing new JWST/NIRSpec observations taken in 2024, 2 years after a first observation with JWST/MIRI. We find that between the two epochs (2022 \& 2024), the CO flux is reduced by a factor $\sim 3$, the flux of the HI 10-6 line seen by both NIRSpec and MIRI is reduced by a factor $\sim13$, and the total continuum density flux is reduced by $\sim 15 \%$. The accretion rate derived from individual HI lines is consistent with a decrease of a factor $\sim13$ in 2 years. After correcting the spectrum from the CO absorption present in J1605 stellar photosphere, we find that the decrease of the disk's CO emission is consistent with a CO gas of same column density and temperature at each epoch, but originating from a smaller emitting area when the accretion rate is low. While warm hydrocarbons ($\simeq 500~$K) are detected with MIRI-MRS with extremely high column densities of $\rm C_2H_2$, no hydrocarbons features are seen with NIRSpec. We propose that non-LTE effects quench the near-IR emission of hydrocarbons in the warm reservoir. The variation of the accretion luminosity of J1605 correlates with the variation of its fundamental CO luminosity in a similar way as in T-Tauri stars, supporting the idea that very-low-mass stars could be seen as scaled-down versions of T-Tauri stars. The detection of the emission of the fundamental band of CO in disks around cold objects is challenging because of the presence of CO absorption in their photosphere. Future observations (e.g., with ELT/METIS) looking for such emission will require robust ways to constrain the photosphere emission.
CommentsAccepted in A&A. 13 pages + 8 pages of Appendix, 10 figures + 9 figures in Appendix
