We present a comprehensive infrared (IR) study of the iconic Wolf-Rayet (WR) wind-blown bubble NGC6888 around WR136. We use Wide-field Infrared Survey Explorer (WISE), Spitzer IRAC and MIPS and Herschel PACS IR images to produce a sharp view of the distribution of dust around WR136. We complement these IR photometric observations with Spitzer IRS spectra in the 5-38 $\mu$m wavelength range. The unprecedented high-resolution IR images allowed us to produce a clean spectral energy distribution, free of contamination from material along the line of sight, to model the properties of the dust in NGC6888. We use the spectral synthesis code Cloudy to produce a model for NGC6888 that consistently reproduces its optical and IR properties. Our best model requires a double distribution with the inner shell composed only of gas, whilst the outer shell requires a mix of gas and dust. The dust consists of two populations of grain sizes, one with small sized grains $a_\mathrm{small}$=[0.002-0.008] $\mu$m and another one with large sized grains $a_\mathrm{big}$=[0.05-0.5] $\mu$m. The population of big grains is similar to that reported for other red supergiants stars and dominates the total dust mass, which leads us to suggest that the current mass of NGC6888 is purely due to material ejected from WR136, with a negligible contribution of swept up interstellar medium. The total mass of this model is 25.5$^{+4.7}_{-2.8}$ M$_{\odot}$, a dust mass of $M_\mathrm{dust}=$0.14$^{+0.03}_{-0.01}$ M$_{\odot}$, for a dust-to-gas ratio of $5.6\times10^{-3}$. Accordingly, we suggest that the initial stellar mass of WR136 was $\lesssim$50 M$_{\odot}$, consistent with current single stellar evolution models.

中文翻译：

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通过红外观测揭示沃尔夫-拉叶星云 NGC 6888 的恒星起源

我们对 WR136 周围标志性的 Wolf-Rayet (WR) 风吹气泡 NGC6888 进行了全面的红外 (IR) 研究。我们使用广域红外巡天探测器 (WISE)、Spitzer IRAC 和 MIPS 以及 Herschel PACS IR 图像生成 WR136 周围尘埃分布的清晰视图。我们用 5-38 $\mu$m 波长范围内的 Spitzer IRS 光谱补充了这些红外光度观测。前所未有的高分辨率红外图像使我们能够产生清晰的光谱能量分布，不受视线沿线材料的污染，以模拟 NGC6888 中灰尘的特性。我们使用光谱合成代码 Cloudy 为 NGC6888 生成一个模型，该模型始终重现其光学和红外特性。我们最好的模型需要内壳仅由气体组成的双重分布，而外壳需要气体和灰尘的混合物。灰尘由两组颗粒大小组成，一组具有小颗粒 $a_\mathrm{small}$=[0.002-0.008] $\mu$m，另一组具有大颗粒 $a_\mathrm{big}$= [0.05-0.5] $\mu$m。大颗粒的数量与其他红超巨星报告的相似，并在总尘埃质量中占主导地位，这使我们认为 NGC6888 的当前质量纯粹是由于 WR136 喷出的物质，对星际掠过的贡献可以忽略不计中等的。该模型的总质量为 25.5$^{+4.7}_{-2.8}$ M$_{\odot}$，尘埃质量为 $M_\mathrm{dust}=$0.14$^{+0.03}_{ -0.01}$ M$_{\odot}$，尘气比为 $5.6\times10^{-3}$。因此，我们建议 WR136 的初始恒星质量为 $\lesssim$50 M$_{\odot}$，