Detection of PAH Absorption and Determination of the Mid-infrared Diffuse Interstellar Extinction Curve from the Sight Line toward Cyg OB2-12
Detection of PAH Absorption and Determination of the Mid-infrared Diffuse Interstellar Extinction Curve from the Sight Line toward Cyg OB2-12
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DOI：
10.3847/1538-4357/ab8cc3
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发表时间：
2020-02
期刊：
影响因子：
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通讯作者：
B. Hensley;B. Draine
中科院分区：
文献类型：
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作者：
B. Hensley;B. Draine
由于天鹅座OB 2 -12的消光系数很大（AV = 10等），而且这种消光似乎是由弥漫的星际介质中的典型尘埃主导的，因此它的视线被广泛用于研究星际尘埃。我们提出了一个新的分析档案红外空间天文台短波长光谱仪和斯皮策IRS的观测天鹅座OB 2 -12使用一个模型的发射从星星和它的恒星风，以确定总消光Aλ从2.4到37 μm。除了突出的9.7和18 μm硅酸盐特征外，我们还稳健地检测到与多环芳烃相关的吸收特征，包括首次识别出吸收中的7.7 μm特征。发现3.3 μm的芳香族特征在吸收中比通常在发射中看到的要宽得多。观测到的3.4和6.85 μm脂肪烃特征的相对强度与在朝向银河系中心的视线上观测到的这些特征一致。我们确定和表征60多个光谱线在这个波长范围内，这可能是有用的约束模型的星星和它的恒星风。基于这一分析，我们提出了一个消光曲线，外推顺利确定平均银河系消光曲线在较短的波长和尘埃不透明度推断在较长的波长发射，提供了一个新的约束模型的星际尘埃中红外。
The sight line toward the luminous blue hypergiant Cyg OB2-12 is widely used to study interstellar dust on account of its large extinction (AV ≃ 10 mag) and the fact that this extinction appears to be dominated by dust typical of the diffuse interstellar medium. We present a new analysis of archival Infrared Space Observatory Short Wavelength Spectrometer and Spitzer IRS observations of Cyg OB2-12 using a model of the emission from the star and its stellar wind to determine the total extinction Aλ from 2.4 to 37 μm. In addition to the prominent 9.7 and 18 μm silicate features, we robustly detect absorption features associated with polycyclic aromatic hydrocarbons, including the first identification of the 7.7 μm feature in absorption. The 3.3 μm aromatic feature is found to be much broader in absorption than is typically seen in emission. The 3.4 and 6.85 μm aliphatic hydrocarbon features are observed with relative strengths that are consistent with observations of these features on sight lines toward the Galactic center. We identify and characterize more than 60 spectral lines in this wavelength range, which may be useful in constraining models of the star and its stellar wind. Based on this analysis, we present an extinction curve that extrapolates smoothly to determinations of the mean Galactic extinction curve at shorter wavelengths and to dust opacities inferred from emission at longer wavelengths, providing a new constraint on models of interstellar dust in the mid-infrared.