发表机构
Chalmers University of Technology; Instituto de Física Fundamental, IFF-CSIC; University of Oslo（查尔姆斯理工大学; 西班牙科学理事会基础物理研究所; 奥斯陆大学）
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ALMA对银河系疏散星团RSGC1和RSGC2中的28颗红超巨星进行分子谱线观测，测量其星周气体性质并估算质量损失率，发现CO发射区异常紧凑，表明星团环境中RSG的星周物质具有独特结构。
AI 中文摘要
我们旨在通过毫米波观测银河系中两个最大的同年龄红超巨星（RSG）群体——疏散星团RSGC1和RSGC2，扩大具有直接星周气体测量的RSG样本。我们利用ALMA对RSGC1和RSGC2中的28颗RSG进行了干涉测量分子谱线研究。主要目标发射是CO J=2-1谱线和连续谱，并对RSGC2目标观测了额外的热SiO和脉泽SiO谱线。我们测量了终端膨胀速度、系统速度、发射区大小，并利用新的长波约束提供了更新的尘埃模型和光度。最后，我们对CO转动谱线发射进行了一维辐射转移建模，以估算质量损失率。我们在RSGC2中的六颗RSG和RSGC1中的五颗RSG中探测到了$^{12}$CO。除DFK 52外，所有$^{12}$CO发射的空间分布相对紧凑或未分辨。获得的质量损失率范围为$\log(\dot{M}/M_\odot\\\\,\mathrm{yr}^{-1})=-5.5$至$-3$，但由于缺乏对包层大小和温度的严格约束，这些值高度不确定。我们获得的质量损失率下限值高于标准经验公式的预测，并支持假设辐射驱动风的尘埃模型。DFK 49是一个明显的异常值：其修正后的光度是两个星团中最低的，但它却拥有一个强风，质量损失率$\dot{M}>10^{-5}\\\\,M_\odot\\\\,\mathrm{yr}^{-1}$。CO发射区域远小于附近RSG和理论模型的预期，表明星团环境中RSG周围的星周物质（CSM）具有独特的相结构。这项工作证明了分子谱线和尘埃观测在约束RSG风方面的相互效用，同时强调了未来需要对RSGC目标进行空间分辨的多示踪剂观测，以确定其星周环境的物理结构并改进质量损失率的测定。
英文摘要
We aim to expand the sample of RSGs with direct measurements of circumstellar gas through millimeter observations of two of the largest coeval RSG populations in the Galaxy: the open clusters RSGC1 and RSGC2. We present an interferometric molecular line study of 28 RSGs in RSGC1 and RSGC2 with ALMA. The primary targeted emission is CO $J=2-1$ and continuum, with additional thermal and maser SiO lines observed for RSGC2 targets. We measure terminal expansion velocities, systemic velocities, emission-region sizes, and provide updated dust models and luminosities using the new long-wavelength constraints. Finally, we perform 1D radiative transfer modeling of CO rotational-line emission to estimate mass-loss rates. We detect $^{12}$CO toward six RSGs in RSGC2 and five in RSGC1. Except for DFK 52, the spatial distribution of all $^{12}$CO emission is relatively compact or unresolved. The obtained mass-loss rates range from $\log(\dot{M}/M_\odot\,\mathrm{yr}^{-1})=-5.5$ to $-3$, but are highly uncertain due to a lack of stringent constraints on the envelope sizes and temperatures. The lower-limit $\dot{M}$-values we obtain are high compared to standard empirical prescriptions and favor dust models assuming a radiatively driven wind. DFK 49 is a clear outlier: its revised luminosity is the lowest in both clusters, yet it harbors a strong wind with $\dot{M}>10^{-5}\,M_\odot\,\mathrm{yr}^{-1}$. The CO emission regions are much smaller than expected from nearby RSGs and theoretical models, and suggest a unique phase structure for the CSM around RSGs in cluster environments. This work demonstrates the mutual utility of molecular line and dust observations for constraining RSG winds, while highlighting the need for future spatially resolved, multi-tracer observations of RSGC targets to establish the physical structure of their circumstellar environments and improve mass-loss determinations.
Comments14 pages, 7 figures, and 2 tables in main body. 8 additional appendix pages with 5 figures and 2 tables. Submitted to A&A
