Spectropolarimetry of the 3.4 μm feature in the diffuse ISM toward the Galactic center quintuplet cluster
Spectropolarimetry of the 3.4 μm feature in the diffuse ISM toward the Galactic center quintuplet cluster
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DOI：
10.1086/507462
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发表时间：
2006-11-01
影响因子：
4.9
通讯作者：
Wright, G.
中科院分区：
文献类型：
--
作者：
Chiar, J. E.;Adamson, A. J.;Wright, G.
脂肪族碳氢化合物在3.4微米处表现出吸收特征，观测到的源是星际介质(ISM)的扩散区。负责这一特征的吸收体被认为存在于星际尘埃的某些成分中，但粒子的物理性质(大小、形状、结构等)。是不确定的。对星际偏振的观测提供了区分。由于携带硅酸盐吸收特征的颗粒已知是对齐的，因此可以利用3.4微米碳氢化合物特征的极化来检验硅酸盐核有机耐火地幔颗粒理论。虽然已经观察到3.4微米的特征在朝向银河系中心的一条视线上没有偏振，但对于同一视线，相应的硅酸盐偏振测量是不可用的。在这里，我们给出了GCS3-II和GCS3-IV向银河系中心的偏振光谱观测，在那里已经观测到了9.7微米的硅酸盐偏振。我们发现，在3.4微米的地物上没有探测到极化，极限分别为0.06%+/-0.13%(GCS3-II)和0.15%+/-0.31%(GCS3-IV)，远低于基于核心-地幔模型的最低可用极化预测。我们的结论是，弥漫的ISM中的碳氢化合物并不与硅酸盐驻留在同一颗粒上，可能形成了一个单独的小颗粒群体。
Aliphatic hydrocarbons exhibit an absorption feature at 3.4 mu m, observed toward sources that sample diffuse regions of the interstellar medium ( ISM). The absorbers responsible for this feature are assumed to reside in some component of interstellar dust, but the physical nature of the particles ( size, shape, structure, etc.) is uncertain. Observations of interstellar polarization provide discrimination. Since the grains that carry the silicate absorption feature are known to be aligned, polarization across the 3.4 mu m hydrocarbon feature can be used to test the silicate-core organic refractory mantle grain theory. Although the 3.4 mu m feature has been observed to be devoid of polarization for one line of sight toward the Galactic center, a corresponding silicate polarization measurement for the same line of sight was not available. Here, we present spectropolarimetric observations of GCS 3-II and GCS 3-IV toward the Galactic center, where the 9.7 mu m silicate polarization has been previously observed. We show that polarization is not detected across the 3.4 mu m feature to a limit of 0.06% +/- 0.13% (GCS 3-II) and 0.15% +/- 0.31% (GCS 3-IV), well below the lowest available prediction of polarization on the basis of the core-mantlemodel. We conclude that the hydrocarbons in the diffuse ISM do not reside on the same grains as the silicates, and likely form a separate population of small grains.