凯克孔径掩蔽实验：尘埃笼罩的红巨星
The Keck Aperture Masking Experiment: Dust Enshrouded Red Giants
摘要：
虽然尘埃渐近巨星分支（AGB）恒星对银河系化学富集的重要性被广泛认可，但对尘埃形成和风驱动机制的复杂理解已被证明是难以捉摸的，部分原因是空间分辨尘埃形成区域本身的困难。作为凯克孔径掩蔽实验的一部分，我们已经观察到了20颗尘埃笼罩的AGB恒星，在1.5微米和3.1微米之间的多个近红外波段中分辨出所有这些恒星。我们发现45%的目标显示出可测量的伸长，当校正目标的更大距离时，将对应于与IRC+10216或CIT 6的著名案例相当的显著不对称的尘埃壳。使用辐射转移模型，我们发现硅酸盐和无定形碳的升华温度分别为1130 +- 90 K和1170 +- 60 K，两者都略低于实验室测量的预期，并且远低于从YSO盘内边缘推断的温度。富O和富C尘埃类型显示出相同的升华温度的事实也令人惊讶。对于最光学厚度的壳（τ> 2，在2.2微米），观察到的内部灰尘壳的温度分布发生了很大的变化，我们建议的效果可能会出现时，个别灰尘团成为光学厚在最高的质量损失率。
英文摘要：
While the importance of dusty asymptotic giant branch (AGB) stars to galactic chemical enrichment is widely recognised, a sophisticated understanding of the dust formation and wind-driving mechanisms has proven elusive due in part to the difficulty in spatially-resolving the dust formation regions themselves. We have observed twenty dust-enshrouded AGB stars as part of the Keck Aperture Masking Experiment, resolving all of them in multiple near-infrared bands between 1.5 microns and 3.1 microns. We find 45% of the targets to show measurable elongations that, when correcting for the greater distances of the targets, would correspond to significantly asymmetric dust shells on par with the well-known cases of IRC+10216 or CIT6. Using radiative transfer models, we find the sublimation temperature of 1130 +- 90 K and 1170 +- 60 K for silicates and amorphous carbon respectively, both somewhat lower than expected from laboratory measurements and vastly below temperatures inferred from the inner edge of YSO disks. The fact that O-rich and C-rich dust types showed the same sublimation temperature was surprising as well. For the most optically-thick shells (tau > 2 at 2.2 microns), the temperature profile of the inner dust shell is observed to change substantially, an effect we suggest could arise when individual dust clumps become optically-thick at the highest mass-loss rates.
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