Temperature Dependence of the Absorption Coefficient of Cosmic Analog Grains in the Wavelength Range 20 Microns to 2 Millimeters
Temperature Dependence of the Absorption Coefficient of Cosmic Analog Grains in the Wavelength Range 20 Microns to 2 Millimeters
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DOI：
10.1086/305415
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发表时间：
1998-04
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影响因子：
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通讯作者：
V. Mennella;J. Brucato;L. Colangeli;Pasquale Palumbo;A. Rotundi;E. Bussoletti
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文献类型：
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作者：
V. Mennella;J. Brucato;L. Colangeli;Pasquale Palumbo;A. Rotundi;E. Bussoletti
在295-24 K温度范围内，测量了20 μm-2 mm的类宇宙尘颗粒、晶态铁橄榄石和镁橄榄石、非晶态铁橄榄石以及两种无序碳颗粒的单位质量吸收系数。结果提供了一个显着的依赖于温度的证据。随着温度的降低，不透明度系统地降低;在1 mm处，从室温到24 K，根据材料的不同，不透明度的变化系数在1.9和5.8之间。无定形晶粒的变化更为显著。吸收系数随波长的变化符合指数β随温度变化的幂律关系。对于两种非晶碳，β（24 K）~1.2，相对于室温值分别增加了24%和50%。发现无定形铁橄榄石增加50%，其特征在于β（24 K）= 2。结晶镁橄榄石β（24 K）= 2.2，铁橄榄石β（24 K）= 2.3，β随温度的变化不明显，分别为14%和10%.对于非晶铁橄榄石颗粒，在24 K的毫米不透明度是一个大的因素~4比结晶对应。此外，还发现了两种结晶硅酸盐红外光谱中红外波段的温度依赖性，随着温度的降低，红外波段的特征变得更加强烈、尖锐，并向稍高的频率移动。结果进行了讨论的内在远红外毫米吸收机制。毫米波吸收与温度的线性关系表明，双声子差过程起主导作用。在这项工作中报告的吸收系数可以是有用的，在获得一个更现实的模拟各种天文数据有关的尘埃在低温下，并给出提示，以更好地确定其实际属性。特别是，他们被用来讨论的起源弥漫远红外毫米星际尘埃发射光谱。提出了由硅酸盐和无定形碳颗粒形成的复合颗粒可以重现观察结果。这些粒子在弥漫介质中的存在与马西斯最近提出的星际消光模型是一致的。
We have measured the absorption coefficient per unit mass of cosmic dust analog grains, crystalline fayalite and forsterite, amorphous fayalite, and two kinds of disordered carbon grains, between 20 μm and 2 mm over the temperature range 295-24 K. The results provide evidence of a significant dependence on temperature. The opacity systematically decreases with decreasing temperature; at 1 mm, it varies by a factor of between 1.9 and 5.8, depending on the material, from room temperature to 24 K. The variations are more marked for the amorphous grains. The wavelength dependence of the absorption coefficient is well fitted by a power law with exponent β that varies with temperature. For the two amorphous carbons, β(24 K) ~1.2 with increases of 24% and 50% with respect to the room-temperature values. A 50% increase is found for amorphous fayalite, characterized by β(24 K) = 2. A less pronounced change of β with temperature, 14% and 10%, is observed for crystalline forsterite, β(24 K) = 2.2, and fayalite, β(24 K) = 2.3, respectively. For amorphous fayalite grains, the millimeter opacity at 24 K is larger by a factor of ~4 than that of the crystalline counterpart. In addition, a temperature dependence of the infrared bands present in the spectrum of the two crystalline silicates is found. The features become more intense, sharpen, and shift to slightly higher frequencies with decreasing temperature. The results are discussed in terms of intrinsic far-infrared-millimeter absorption mechanisms. The linear dependence of the millimeter absorption on temperature suggests that two-phonon difference processes play a dominant role. The absorption coefficients reported in this work can be useful in obtaining a more realistic simulation of a variety of astronomical data concerning dust at low temperatures and give hints to better identify its actual properties. In particular, they are used to discuss the origin of the diffuse far-infrared-millimeter interstellar dust emission spectrum. It is proposed that composite particles formed of silicate and amorphous carbon grains can reproduce the observations. The presence of these particles in the diffuse medium is consistent with the recent interstellar extinction model by Mathis.