Title: On the alumina dust production in the winds of O-rich Asymptotic Giant Branch stars Show Chinese title

Title: 在富氧渐近巨星分支恒星风中的氧化铝尘埃生产

Abstract: The O-rich Asymptotic Giant Branch (AGB) stars experience strong mass loss with efficient dust condensation and they are major sources of dust in the interstellar medium. Alumina dust (Al$_2$O$_3$) is an important dust component in O-rich circumstellar shells and it is expected to be fairly abundant in the winds of the more massive and O-rich AGB stars. By coupling AGB stellar nucleosynthesis and dust formation, we present a self-consistent exploration on the Al$_2$O$_3$ production in the winds of AGB stars with progenitor masses between $\sim$3 and 7 M$_{\odot}$ and metallicities in the range 0.0003 $\le$ Z $\le$ 0.018. We find that Al$_2$O$_3$ particles form at radial distances from the centre between $\sim2$ and 4 R$_*$ (depending on metallicity), which is in agreement with recent interferometric observations of Galactic O-rich AGB stars. The mass of Al$_2$O$_3$ dust is found to scale almost linearly with metallicity, with solar metallicity AGBs producing the highest amount (about 10$^{-3}$ M$_{\odot}$) of alumina dust. The Al$_2$O$_3$ grain size decreases with decreasing metallicity (and initial stellar mass) and the maximum size of the Al$_2$O$_3$ grains is $\sim$0.075 $\mu m$ for the solar metallicity models. Interestingly, the strong depletion of gaseous Al observed in the low-metallicity HBB AGB star HV 2576 seems to be consistent with the formation of Al$_2$O$_3$ dust as predicted by our models. We suggest that the content of Al may be used as a mass (and evolutionary stage) indicator in AGB stars experiencing HBB. Show Chinese abstract

Abstract: 富含氧的渐近巨星分支（AGB）恒星经历强烈的质量损失，伴有高效的尘埃凝聚，它们是星际介质中的主要尘埃来源。 氧化铝尘埃（Al$_2$O$_3$）是富含氧的星周壳层中的重要尘埃成分，预计在更大质量和富含氧的AGB恒星的风中相对丰富。 通过耦合AGB恒星的核合成和尘埃形成，我们对祖恒星质量在$\sim$3到7 M$_{\odot}$之间、金属丰度范围为0.0003$\le$Z$\le$0.018的AGB恒星风中Al$_2$O$_3$的产生进行了自洽的探讨。 我们发现Al$_2$O$_3$粒子在中心的径向距离之间形成$\sim2$和4 R$_*$（取决于金属量），这与最近对银河系富氧AGB星的干涉观测结果一致。 铝$_2$O$_3$灰尘的质量被发现几乎与金属量成线性比例，太阳金属量的AGB星产生最多的氧化铝灰尘（约10$^{-3}$ M$_{\odot}$）。 Al$_2$O$_3$颗粒尺寸随着金属量（以及初始恒星质量）的降低而减小，Al$_2$O$_3$颗粒的最大尺寸在太阳金属量模型中为$\sim$0.075 $\mu m$。 有趣的是，在低金属量的HBB AGB恒星HV 2576中观察到的气态铝强烈耗竭似乎与我们的模型预测的Al$_2$O$_3$粉尘形成一致。 我们建议，铝的含量可能用作经历HBB的AGB恒星的质量（和演化阶段）指示器。