The sightline toward the luminous blue hypergiant Cyg OB2-12 is widely used in studying interstellar dust on account of its large extinction ($A_V \simeq 10$ 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 ISO-SWS 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 $A_\lambda$ from 2.4--37 $\mu$m. In addition to the prominent 9.7 and 18 $\mu$m silicate features, we robustly detect absorption features associated with polycyclic aromatic hydrocarbons (PAHs), including the first identification of the 7.7 $\mu$m feature in absorption. The 3.3 $\mu$m aromatic feature is found to be much broader in absorption than is typically seen in emission. The 3.4 and 6.85 $\mu$m aliphatic hydrocarbon features are observed with relative strengths consistent with observation of these features on sightlines toward the Galactic Center. We identify and characterize more than sixty 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 $A_\lambda/A_{2.2 \mu m}$ 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.

中文翻译：

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PAH 吸收的检测和从视线到 Cyg OB2-12 的中红外漫射星际消光曲线的确定

由于它的大灭绝（$A_V \simeq 10$ mag）和这种灭绝似乎主要是由弥漫性星际的典型尘埃所支配的事实，朝向发光的蓝色超巨星 Cyg OB2-12 的视线被广泛用于研究星际尘埃中等的。我们对 Cyg OB2-12 的档案 ISO-SWS 和 Spitzer IRS 观测进行了新的分析，使用恒星及其恒星风的发射模型来确定从 2.4--37 $\mu 的总灭绝 $A_\lambda$ $米。除了突出的 9.7 和 18 $\mu$m 硅酸盐特征外，我们还稳健地检测了与多环芳烃 (PAH) 相关的吸收特征，包括首次识别出 7.7 $\mu$m 的吸收特征。发现 3.3 $\mu$m 芳香特征的吸收比通常在发射中看到的要广泛得多。3.4 和 6。85 $\mu$m 脂肪烃特征被观察到，其相对强度与在朝向银河中心的视线上观察到的这些特征一致。我们在这个波长范围内识别和表征了 60 多条光谱线，这可能有助于约束恒星及其恒星风的模型。基于这一分析，我们提出了一条消光曲线 $A_\lambda/A_{2.2 \mu m}$，该曲线可以平滑地外推到较短波长下平均银河消光曲线的确定以及从较长波长发射推断出的尘埃不透明度，提供了中红外星际尘埃模型的新约束。我们在这个波长范围内识别和表征了 60 多条光谱线，这可能有助于约束恒星及其恒星风的模型。基于这一分析，我们提出了一条消光曲线 $A_\lambda/A_{2.2 \mu m}$，该曲线可以平滑地外推到较短波长下平均银河消光曲线的确定以及从较长波长发射推断出的尘埃不透明度，提供了中红外星际尘埃模型的新约束。我们在这个波长范围内识别和表征了 60 多条光谱线，这可能有助于约束恒星及其恒星风的模型。基于这一分析，我们提出了一条消光曲线 $A_\lambda/A_{2.2 \mu m}$，该曲线可以平滑地外推到较短波长下平均银河消光曲线的确定以及从较长波长发射推断出的尘埃不透明度，提供了中红外星际尘埃模型的新约束。