Title: Infrared Study of Fullerene Planetary Nebulae Show Chinese title

Title: 红外线研究富勒烯行星状星云

Abstract: We present a study of 16 PNe where fullerenes have been detected in their Spitzer spectra. This large sample of objects offers an unique opportunity to test conditions of fullerene formation and survival under different metallicity environments as we are analyzing five sources in our own Galaxy, four in the LMC, and seven in the SMC. Among the 16 PNe under study, we present the first detection of C60 (possibly also C70) fullerenes in the PN M 1-60 as well as of the unusual 6.6, 9.8, and 20 um features (possible planar C24) in the PN K 3-54. Although selection effects in the original samples of PNe observed with Spitzer may play a potentially significant role in the statistics, we find that the detection rate of fullerenes in C-rich PNe increases with decreasing metallicity (5% in the Galaxy, 20% in the LMC, and 44% in the SMC). CLOUDY photoionization modeling matches the observed IR fluxes with central stars that display a rather narrow range in effective temperature (30,000-45,000 K), suggesting a common evolutionary status of the objects and similar fullerene formation conditions. The observed C60 intensity ratios in the Galactic sources confirm our previous finding in the MCs that the fullerene emission is not excited by the UV radiation from the central star. CLOUDY models also show that line- and wind-blanketed model atmospheres can explain many of the observed [NeIII]/[NeII] ratios by photoionization suggesting that possibly the UV radiation from the central star, and not shocks, are triggering the decomposition of the circumstellar dust grains. With the data at hand, we suggest that the most likely explanation for the formation of fullerenes and graphene precursors in PNe is that these molecular species are built from the photo-chemical processing of a carbonaceous compound with a mixture of aromatic and aliphatic structures similar to that of HAC dust. Show Chinese abstract

Abstract: 我们研究了16个行星状星云（PNe），其中在它们的斯皮策光谱中检测到了富勒烯。这一庞大的天体样本为我们提供了一个独特的机会，可以在不同金属丰度环境中测试富勒烯形成和存活的条件，因为我们正在分析银河系中的五个源，大麦哲伦云（LMC）中的四个源，以及小麦哲伦云（SMC）中的七个源。在研究的16个PNe中，我们首次在M 1-60 PNe中检测到C60（可能还有C70）富勒烯，并且在K 3-54 PNe中检测到不寻常的6.6、9.8和20微米特征（可能是平面C24）。尽管斯皮策观测原始样本中的选择效应可能在统计学上起潜在的重要作用，但我们发现富勒烯在碳丰富的PNe中的检出率随着金属丰度的降低而增加（银河系中为5％，LMC中为20％，SMC中为44％）。CLOUDY光致电离建模与有效温度范围相对较窄（30,000-45,000 K）的中心星所观测到的红外流量相匹配，表明这些天体具有共同的演化状态和相似的富勒烯形成条件。银河系源观测到的C60强度比值证实了我们在Magellanic Clouds中的先前发现，即富勒烯发射并非由中心星的紫外辐射激发。CLOUDY模型还显示，带有线和风遮罩的模型大气可以通过光致电离解释许多观测到的[NeIII]/[NeII]比值，这表明可能是中心星的紫外辐射，而不是冲击波，触发了周围星际尘埃颗粒的分解。根据现有数据，我们认为PNe中富勒烯和石墨烯前驱体形成的最可能解释是这些分子物种是由碳质化合物通过光化学处理产生的，这种化合物具有类似HAC尘埃的芳香族和脂肪族结构混合物。