生锈的老恒星：失踪的星际铁的来源？
Rusty old stars: a source of the missing interstellar iron?
摘要：
铁是宇宙中最丰富的耐火元素，在星周和星际环境中都高度耗尽，这意味着它以固体形式存在。这种固体的性质是未知的。在这封信中，我们提供的证据表明，金属铁颗粒存在于富氧的AGB恒星周围，在那里它被观测为一个无特征的中红外线过剩。这一识别是利用斯皮策太空望远镜对演化的球状星团恒星的观测做出的，在这些恒星中，铁尘的产生似乎无处不在，在某些情况下可以被建模为唯一观测到的尘埃产物。在这种情况下，FeO被视为在这些恒星中观察到的20微米特征的可能载体。金属铁在低金属度的尘埃凝聚序列中起着重要的作用，并在星际介质中起着重要的作用。我们将探讨恒星的金属丰度和光度在铁的形成观察，以及如何铁的存在影响流出和它的化学。铁能提供足够的不透明度来驱动风的条件仍然不清楚。
英文摘要：
Iron, the Universe's most abundant refractory element, is highly depleted in both circumstellar and interstellar environments, meaning it exists in solid form. The nature of this solid is unknown. In this Letter, we provide evidence that metallic iron grains are present around oxygen-rich AGB stars, where it is observationally manifest as a featureless mid-infrared excess. This identification is made using Spitzer Space Telescope observations of evolved globular cluster stars, where iron dust production appears ubiquitous and in some cases can be modelled as the only observed dust product. In this context, FeO is examined as the likely carrier for the 20-micron feature observed in some of these stars. Metallic iron appears to be an important part of the dust condensation sequence at low metallicity, and subsequently plays an influential role in the interstellar medium. We explore the stellar metallicities and luminosities at which iron formation is observed, and how the presence of iron affects the outflow and its chemistry. The conditions under which iron can provide sufficient opacity to drive a wind remain unclear.
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