低质量红巨星中的可变质量损失：47 Tuc 恒星演化过程中的色球层运动
The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc
- Universidad Andrés Bello（安德烈斯贝略大学）
- European Southern Observatory（欧洲南方天文台）
- Osservatorio Astronomico di Padova-INAF（帕多瓦天文台-意大利国家天体物理研究所）
- Università degli Studi di Bologna（博洛尼亚大学）
- INAF – Osservatorio di astrofisica e scienza dello spazio di Bologna（意大利国家天体物理研究所-博洛尼亚天文与空间科学观测站）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究通过47 Tuc星团红巨星Hα光谱监测，发现色球层变化随光度增强并出现外流迹象，特征时间尺度约一天，为理解低质量巨星质量损失提供了观测约束。
AI中文摘要：
质量损失（ML）是一个关键过程，尽管其在天体物理学中具有广泛影响，但至今仍未被充分理解。我们目前的知识不足以在不同恒星中一致地再现质量损失，尤其是在冷且低质量的巨星中，色球层（CHR）——预计在该区域中驱动质量损失的大多数物理现象发生的地方——的时间变化特性受到的限制很差。我们表征了红巨星中色球层变性的相关时间尺度，并探索了其与恒星内在属性的相关性。我们利用FLAMES/GIRAFFE数据，分析了球状星团NGC 104（47 Tuc）中红巨星Hα线色球层变性的首次大规模时间光谱监测。我们发现，Hα变化随光度平均增加并跨越更宽的值范围，同时线芯系统性蓝移，表明对于log(L/L☉) ≳ 2.4存在外流，以及更深的线芯与增加的色球层光学深度一致。观察Hα轮廓变化所需的特征时间尺度约为一天，随光度呈平坦趋势。虽然较短时间尺度的变化仍与统计不确定性一致，但发现朝向较暗恒星可能存在增加。这些趋势似乎与光度和有效温度相似地相关。未发现与不同星族有进一步相关性，也未在AGB和RGB恒星之间观察到显著差异。外流趋势与先前在广泛金属丰度范围内的观测结果紧密匹配。我们讨论了这些观测是否反映了Hα对风敏感性的变化、由加热效率变化驱动的真实大气转变，或持续色球层膨胀且Hα形成受几何学主导。
英文摘要：
Mass-Loss (ML) is a critical process that remains poorly understood despite its broad implications across astrophysics. Our current knowledge is insufficient to reproduce ML consistently across stars, particularly in cool, low-mass giants, where the time-variable nature of chromospheres (CHR) ---the region where most physical phenomena powering ML in this regime are expected to occur--- is poorly constrained. We characterize the relevant timescales of CHR variability in red giants and explore correlations with intrinsic stellar properties. We analyze the first large temporal spectroscopic monitoring of CHR variability using the H$α$ line in red giants belonging to the globular cluster NGC 104 (47 Tuc) using FLAMES/GIRAFFE data. We find that H$α$ variations increase on average and span a wider range of values with luminosity, together with a systematic blueshift of the line core indicative of outflows for $\log(L/L_\odot) \gtrsim 2.4$, alongside deeper cores consistent with increased CHR optical depth. The characteristic timescale required to observe variations in the H$α$ profile is approximately one day, showing a flat trend with luminosity. While shorter-timescale variations remain consistent with statistical uncertainties, a possible increase toward dimmer stars is found. These trends appear similarly correlated with luminosity and effective temperature. No further correlation is found with different cluster populations, nor are significant differences observed between AGB and RGB stars. The outflow trends closely match previous observations across a wide metallicity range. We discuss whether these observations reflect changes in H$α$ sensitivity to the winds, a genuine atmospheric transition driven by changes in heating efficiency, or continued CHR expansion with geometrically dominated H$α$ formation.
