一氧化二铁纳米粒子作为后渐近巨分支星21微米神秘辐射特征的载体
On Iron Monoxide Nanoparticles as a Carrier of the Mysterious 21 Micrometer Emission Feature in Post-Asymptotic Giant Branch Stars
摘要：
一个突出的，神秘的发射特征峰值在~20.1微米-历史上被称为"21微米“特征-在二十多个银河系和麦哲伦云富碳后渐近巨星分支（后AGB）恒星中被发现。自1989年首次探测到21微米特征以来，其载体的性质仍然未知。已经提出了十几种材料作为可能的载体候选物。然而，它们都没有被接受：它们要么需要太多的材料（与这些后AGB恒星周围的拱星壳相比），要么表现出额外的发射特征，这些特征在这些21微米的来源中看不到。最近，一氧化二铁（FeO）纳米粒子似乎是一个有前途的候选载体，因为铁是一个丰富的元素和FeO发射专门在~21微米。在这项工作中，使用原型的原行星状星云HD 56126作为测试案例，我们研究FeO纳米粒子作为载体的21微米的功能，通过模拟他们的红外发射，与FeO被stochemical加热的单恒星光子。我们发现，FeO发出太宽的21微米的功能，以解释所观察到的一个和铁的丰度需要锁定在FeO超过HD 56126中可用。因此，我们得出结论，FeO纳米粒子是不可能负责的21微米的功能。
英文摘要：
A prominent, mysterious emission feature peaking at ~20.1 micrometer --- historically known as the ``21 micrometer' feature --- is seen in over two dozen Galactic and Magellanic Cloud carbon-rich post-asymptotic giant branch (post-AGB) stars. The nature of its carrier remains unknown since the first detection of the 21 micrometer feature in 1989. Over a dozen materials have been suggested as possible carrier candidates. However, none of them has been accepted: they either require too much material (compared to what is available in the circumstellar shells around these post-AGB stars), or exhibit additional emission features which are not seen in these 21 micrometer sources. Recently, iron monoxide (FeO) nanoparticles seem to be a promising carrier candidate as Fe is an abundant element and FeO emits exclusively at ~21 micrometer. In this work, using the proto-typical protoplanetary nebula HD 56126 as a test case, we examine FeO nanoparticles as a carrier for the 21 micrometer feature by modeling their infrared emission, with FeO being stochastically heated by single stellar photons. We find that FeO emits too broad a 21 micrometer feature to explain the observed one and the Fe abundance required to be locked up in FeO exceeds what is available in HD 56126. We therefore conclude that FeO nanoparticles are unlikely responsible for the 21 micrometer feature.
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