Evolution of dust properties in an interstellar filament
Evolution of dust properties in an interstellar filament
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星际细丝中尘埃特性的演变
DOI：
10.1051/0004-6361:20021309
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发表时间：
2003
影响因子：
6.5
通讯作者：
J. Torre
中科院分区：
文献类型：
--
作者：
B. Stepnik;A. Abergel;J. Bernard;F. Boulanger;L. Cambrésy;M. Giard;A. Jones;G. Lagache;J. Lamarre;C. Meny;F. Pajot;F. L. Peintre;I. Ristorcelli;G. Serra;J. Torre
本文介绍了利用球载实验PRONAOS/SPM获得的金牛座分子复合物中静态密丝（通常为$A_{V} \sim 4$）在200至600 μ m范围内的亚毫米观测结果，角分辨率为2-3.5 '。像许多其他分子云一样，与弥漫星际介质相比，这种细丝在其IRAS $I_{\rm 60 \,\mu m}/I_{\rm 100 \,\mu m}$通量比中表现出缺陷。结合PRONAOS/SPM和IRAS数据，我们发现，在灯丝内部，没有证据表明瞬时加热的小颗粒负责60 μ m发射，并且在灯丝内部与辐射场处于热平衡的大颗粒的温度降低了。温度低至12.1 $^{+0.2}_{-0.1}$ K与$\beta=1.9\pm 0.2$（或12.0 $^{+0.2}_{-0.1}$ K使用$\beta=2$）向灯丝中心。这些现象是负责的IRAS色比观察到的灯丝。为了解释这种寒冷的温度，我们开发了一个模型，利用2MASS星表中的恒星计数作为总柱密度的独立示踪剂和辐射传输代码，从灯丝发射。我们首先使用了Desert等人的标准模型中尘埃的光学特性。计算出的亮度曲线无法再现灯丝内部的数据，这表明尘埃的性质在灯丝内部发生了变化。通过从灯丝最密集的部分去除所有瞬时加热的颗粒，并将亚毫米发射率乘以一个重要因子3.4 $^{+0.3}_{-0.7}$（通常为$n_{H}> 3 \pm 1\times 10^3$ cm - 3,$A_{V} > 2.1\pm 0.5$），可以发现数据和模型之间的一致性。我们发现，细丝内部可能发生颗粒-颗粒凝聚成蓬松的聚集体，这解释了小颗粒丰度的缺陷和大颗粒亚毫米发射率的增强。
We present submillimetre observations obtained using the balloon-borne experiment PRONAOS/SPM, from 200 to 600 μ m with an angular resolution of 2–3.5′, of a quiescent dense filament (typically $A_{V} \sim 4$) in the Taurus molecular complex. This filament, like many other molecular clouds, presents a deficit in its IRAS $I_{\rm 60 \,\mu m}/I_{\rm 100 \,\mu m}$ flux ratio in comparison with the diffuse interstellar medium. We show, from the combination of the PRONAOS/SPM and IRAS data, that, inside the filament, there is no evidence for emission from the transiently heated small particles responsible for the 60 μ m emission, and that the temperature of large grains in thermal equilibrium with the radiation field is reduced in the inner parts of the filament. The temperature is as low as 12.1$^{+0.2}_{-0.1}$ K with $\beta=1.9\pm 0.2$ (or 12.0$^{+0.2}_{-0.1}$ K using $\beta=2$) toward the filament centre. These phenomena are responsible for the IRAS colour ratio observed toward the filament. In order to explain this cold temperature, we have developed a model for the emission from the filament using star counts from the 2MASS catalog as an independent tracer of the total column density and a radiative transfer code. We first use the optical properties of the dust from the standard model of Desert et al. ([CITE]). The computed brightness profiles fail to reproduce the data inside the filament, showing that the dust properties change inside the filament. An agreement between data and model can be found by removing all the transiently heated particles from the densest parts of the filament, and multiplying the submillimetre emissivity by a significant factor, 3.4$^{+0.3}_{-0.7}$ (for typically $n_{H}> 3 \pm 1\times 10^3$ cm -3 , $A_{V} > 2.1\pm 0.5$). We show that grain-grain coagulation into fluffy aggregates may occur inside the filament, explaining both the deficit of small grain abundance and the submillimetre emissivity enhancement of the large grains.