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arXiv 1909.00652astro-ph.GAastro-ph.HEcond-mat.mtrl-sci
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Interstellar dust沿GX 3+1视线

Interstellar dust along the line of sight of GX 3+1

D. Rogantini, E. Costantini, S. T. Zeegers, C. P. de Vries, M. Mehdipour, F. de Groot, H. Mutschke, I. Psaradaki, L. B. F. M. Waters

摘要:

通过研究星际尘埃颗粒对X射线辐射的吸收和散射,我们可以了解宇宙颗粒的物理和化学性质,即使是在银河系的致密区域。我们的目标是在钱德拉X射线天文台覆盖的能带中呈现出清晰的吸收特征的尘埃硅酸盐人口的特征。通过这些吸收特征,原则上可以推断出星际介质中硅酸盐的粒度分布、成分和结构。特别是,在这项工作中,我们调查镁和硅的K-边缘。通过使用新获得的同步辐射测量,我们建立了15个尘埃候选者的X射线消光模型。这些模型适用于天体物理分析,并在Spex光谱拟合程序中实现,用于再现明亮的低质量X射线双星GX 3+1的光谱中观察到的尘埃吸收特征,这是用作背景源。同时分析的两个边缘,我们测试两种不同的尺寸分布的灰尘:一个对应于标准的Mathis-Rumpl-Nordsieck模型和一个考虑较大的颗粒($n(a) \propto a_i^{-3.5}$与$0.005<a_1<0.25$和$0.05<a_2<0.5$,分别与$a$的颗粒大小)。这些分布可能代表了朝向该源的复杂银河系区域。我们发现,高达$70\%$的灰尘是由无定形橄榄石。我们将讨论沿着这条视线发现的宇宙尘埃的结晶度。镁和硅都在尘埃中高度贫化(分别为$δ_{Z} = 0.89\ \rm{and}\ 0.94$),而它们的总丰度并不偏离太阳值。

英文摘要:

Studying absorption and scattering of X-ray radiation by interstellar dust grains allows us to access the physical and chemical properties of cosmic grains even in the densest regions of the Galaxy. We aim at characterising the dust silicate population which presents clear absorption features in the energy band covered by the Chandra X-ray Observatory. Through these absorption features, in principle, it is possible to infer the size distribution, composition, and structure of silicate in the interstellar medium. In particular, in this work, we investigate the magnesium and silicon K-edges. By using newly acquired synchrotron measurements, we build X-ray extinction models for fifteen dust candidates. These models, adapted for astrophysical analysis, and implemented in the Spex spectral fitting program, are used to reproduce the dust absorption features observed in the spectrum of the bright low mass X-ray binary GX 3+1 which is used as a background source. With the simultaneous analysis of the two edges we test two different size distributions of dust: one corresponding to the standard Mathis-Rumpl-Nordsieck model and one considering larger grains ($n(a) \propto a_i^{-3.5}$ with $0.005<a_1<0.25$ and $0.05<a_2<0.5$, respectively, with $a$ the grain size). These distributions may be representative of the complex Galactic region towards this source. We find that up to $70\%$ of dust is constituted by amorphous olivine. We discuss the crystallinity of the cosmic dust found along this line of sight. Both magnesium and silicon are highly depleted into dust ($δ_{Z} = 0.89\ \rm{and}\ 0.94$, respectively) while their total abundance does not depart from solar values.

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