标题： 米拉（$o$ Ceti）尘核形成的观测研究：I. AlO及其他含铝物种的可变特征 显示英文标题

标题： An observational study of dust nucleation in Mira ($o$ Ceti): I. Variable features of AlO and other Al-bearing species

摘要： 背景：尘埃由冷巨星高效产生，但无机尘埃的凝结机制尚不清楚。 目的：识别并表征米拉星（$o$Ceti）周围的星际气体中的含铝物种，以阐明它们在生产Al$_2$O$_3$尘埃中的作用。 方法：多历元光谱线观测，包括亚毫米、远红外和光学波段：使用ALMA探测距离恒星约30毫角秒范围内气体分布的地图；2013-2015年使用ALMA、APEX和赫歇尔对含铝分子旋转线的周期性和周期间变化进行观测；追溯到1965年的光学记录，用于检查数天至数十年时间跨度内的电子跃迁变化；以及对光谱特征的速度测量和激发分析，以约束气体的物理参数。 结果：三原子分子AlO、AlOH和AlH，以及原子Al I是米拉星中最主要的可观察到的含铝物种，尽管大量铝可能存在于尚未被识别的其他物种中。 AlO的亚毫米和光学特征的强烈不规则变化（可能是Al$_2$O$_3$的直接前体）表明激发条件发生了显著变化，或者与恒星中的激波相关的丰度变化。 AlO的非均匀分布可能影响尘埃生产的时空特性。 结论：我们无法定量追踪气相中的铝耗尽，但丰富的观测数据限制了随时间变化的化学网络。 未来改进应包括更高阶含铝氧化物的光谱特征分析、不同变率阶段的尘埃和气体物种的协调观测，以及推导激波激发气体中丰度的工具。 显示英文摘要

摘要： Context: Dust is efficiently produced by cool giant stars, but the condensation of inorganic dust is poorly understood. Aims: Identify and characterize aluminum bearing species in the circumstellar gas of Mira ($o$ Ceti) in order to elucidate their role in the production of Al$_2$O$_3$ dust. Methods: Multiepoch spectral line observations at (sub-)millimeter, far-infrared, and optical wavelengths including: maps with ALMA which probe the gas distribution in the immediate vicinity of the star at ~30 mas; observations with ALMA, APEX, and Herschel in 2013-2015 for studying cycle and inter-cycle variability of the rotational lines of Al bearing molecules; optical records as far back as 1965 to examine variations in electronic transitions over time spans of days to decades; and velocity measurements and excitation analysis of the spectral features which constrain the physical parameters of the gas. Results: Three diatomic molecules AlO, AlOH, and AlH, and atomic Al I are the main observable aluminum species in Mira, although a significant fraction of aluminum might reside in other species that have not yet been identified. Strong irregular variability in the (sub-)millimeter and optical features of AlO (possibly the direct precursor of Al$_2$O$_3$) indicates substantial changes in the excitation conditions, or varying abundance that is likely related to shocks in the star. The inhomogeneous distribution of AlO might influence the spatial and temporal characteristics of dust production. Conclusions: We are unable to quantitatively trace aluminum depletion from the gas, but the rich observational material constrains time dependent chemical networks. Future improvements should include spectroscopic characterization of higher aluminum oxides, coordinated observations of dust and gas species at different variability phases, and tools to derive abundances in shock excited gas.