利用变星和H$_2$O打破AGB颜色简并：AGB化学、尘埃和J区在不同环境中的一致图像
Breaking the AGB Color Degeneracy with Variability and H$_2$O: A Consistent Picture of AGB Chemistry, Dust, and the J-Region Across Environments
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中文总结 AI 辅助
本研究利用脉动、H2O吸收和红外超额，揭示AGB恒星化学分类与尘埃产生的环境依赖性，挑战J区标准烛光的普适性，并提出结合变率与分子特征测光改进分类的方法。
中文摘要 AI 辅助
已分辨的渐近巨分支（AGB）星群呈现许多观测难题。我们考虑了三个通常被分开处理的问题：光度的C/O分类边界必须在新的环境中经验性地重新划定；静水压模型网格在采样H2O吸收的波段中过蓝；以及J区（JAGB）光度在单个星系的不同区域之间可能存在差异。脉动将它们联系成一个连贯的图像。利用SPHEREx对麦哲伦星云（LMC）中AGB恒星的光谱观测，结合JWST/NIRCam测光和SN Ia宿主星系M101的HST时间序列，并通过合成测光将它们置于共同尺度上，我们研究了AGB变率、表面化学和星周尘埃如何依赖于环境。我们开发了一个对1.9微米H2O吸收敏感的F182M指数，该指数能对变AGB恒星进行化学分类，并揭示在宽带颜色中与富碳（C-rich）恒星简并的富氧（O-rich）恒星。由于这些特征产生于延伸的大气层中，静水压模型难以重现它们。脉动和星周尘埃呈不对称关联：几乎所有具有显著红外超额的恒星都是变星，而许多变星却显示出很少的尘埃。这支持了由脉动引发并由尘埃形成增强的质量损失。M101中的富氧变AGB恒星在尘埃敏感颜色上比LMC中的对应恒星红约0.7星等，这与在较高金属丰度下更有效的硅酸盐尘埃产生一致，而富碳星群对环境依赖性较小。因此，在LMC中能干净选择富碳恒星的颜色窗口在富金属的M101中有33-68%是富氧的。这对J区作为标准烛光的普适性提出了挑战，同时规避了标准的自洽性检查。我们建议将变率（或暗示变率的红外超额）与分子特征测光相结合，以改进在0.75-5.0微米范围内的AGB分类。
英文摘要
Resolved asymptotic giant branch (AGB) populations present many observational puzzles. We consider three often treated separately: photometric C/O classification boundaries must be redrawn empirically in new environments; hydrostatic model grids are too blue in bands sampling H2O absorption; and J-region (JAGB) luminosities can differ between fields of a single galaxy. Pulsation connects them into a coherent picture. Using SPHEREx spectroscopy of AGB stars in the Large Magellanic Cloud (LMC) with JWST/NIRCam photometry and HST time-series of the SN Ia host M101, placed on a common scale by synthetic photometry, we investigate how AGB variability, surface chemistry, and circumstellar dust depend on environment. We develop an F182M index sensitive to 1.9$μ$m H2O absorption that chemically classifies variable AGB stars and reveals oxygen-rich (O-rich) stars degenerate with carbon-rich (C-rich) stars in broadband colors. Because these features arise in extended atmospheric layers, hydrostatic grids struggle to reproduce them. Pulsation and circumstellar dust are asymmetrically linked: nearly all stars with substantial infrared excess are variable, while many variables show little dust. This supports mass loss initiated by pulsation and enhanced by dust formation. Variable O-rich AGB stars in M101 are up to ~0.7 mag redder than their LMC counterparts in dust-sensitive colors, consistent with more efficient silicate-dust production at higher metallicity, while C-rich populations depend less on environment. Color windows that select C-rich stars cleanly in the LMC are therefore 33-68% O-rich in the metal-rich M101. This challenges the J-region's universality as a standard candle while evading standard self-consistency checks. We recommend combining variability, or the infrared excess that implies it, with photometry of molecular features to improve AGB classification at 0.75-5.0$μ$m.
发表机构
- Center for Astrophysics — Harvard & Smithsonian（天体物理中心——哈佛大学与史密森尼学会）
- Florida State University（佛罗里达州立大学）
- The Johns Hopkins University（约翰斯·霍普金斯大学）
- Space Telescope Science Institute（太空望远镜科学研究所）
- European Space Agency (ESA)（欧洲空间局）
- South African Astronomical Observatory（南非天文台）
机构由 AI 辅助整理，请以论文原文为准。
