氢化非晶碳颗粒作为富勒烯行星状星云 Tc 1 中 9–13 μm 平台特征的可能载体
Hydrogenated amorphous carbon grains as an alternative carrier of the 9$-$13$μ$m plateau feature in the fullerene planetary nebula Tc 1
AI总结：
本文首次在光致电离模型中引入 300 K 氢化非晶碳颗粒的光学常数，成功再现 Tc 1 的 12 μm 平台特征，提出 HAC 类颗粒可能是该特征载体并与富勒烯形成机制相关。
摘要：
自从在行星状星云 Tc 1 的中红外光谱中发现 C₆₀ 以来，天文学家已在多个天体对象中观测到富勒烯。此前研究提出，宽未证认红外（UIR）平台特征——例如 9–13 μm 发射特征（下文简称 12 μm 特征）——的载体可能与富勒烯的形成有关，并进一步认为其载体可能是混合芳香族或脂肪族碳氢化合物，例如氢化非晶碳（下文简称 HAC 类）颗粒。本研究使用光致电离代码对含 C₆₀ 的行星状星云 Tc 1 的中红外发射进行建模，并首次引入 300 K 下 HAC 类尘埃的实验室光学常数（n 和 k 折射率）。有趣的是，我们发现采用标准 HAC 颗粒的分布可以很好地再现 Tc 1 中宽阔的 12 μm 平台特征；同时，这些颗粒还提供了红外尘埃连续谱发射的重要部分，并与观测到的其他 UIR 特征（例如宽阔的 6–9 μm 平台特征）相符。这一发现表明，HAC 类颗粒可能是 12 μm 平台特征的载体，并且很可能与行星状星云中富勒烯的形成机制有关。我们强烈鼓励开展更多实验室实验，以获得不同结构或不同物理条件下成分各异的 HAC 类尘埃的光学常数，从而将这项初步研究扩展到更多含富勒烯的行星状星云，并揭示富勒烯形成的细节以及难以捉摸的 UIR 平台特征的潜在载体。
英文摘要：
Fullerenes have been observed in several astronomical objects since the discovery of C$_{60}$ in the mid-infrared (mid-IR) spectrum of the planetary nebula (PN) Tc 1. It has been suggested that the carriers of the broad unidentified infrared (UIR) plateau features, such as the 9$-$13$μ$m emission feature (12$μ$m hereafter), may be related to the formation of fullerenes. In particular, their carriers have been suggested to be mixed aromatic or aliphatic hydrocarbons such as hydrogenated amorphous carbon (HAC-like hereafter) grains. For this study, we modeled the mid-IR emission of the C$_{60}$-PN Tc 1 with a photoionization code, including for the first time the laboratory optical constants ($n$ and $k$ indices) of HAC-like dust at 300 K. Interestingly, we find that the broad 12$μ$m plateau feature in Tc 1 is well reproduced by using a distribution of canonical HAC grains, while at the same time they provide an important fraction of the IR dust continuum emission and are consistent with the other UIR features observed (e.g., the broad 6$-$9$μ$m plateau feature). This finding suggests that HAC-like grains may be possible carriers of the 12$μ$m plateau feature, being likely related to the fullerene formation mechanism in PNe. More laboratory experiments, to obtain the optical constants of HAC-like dust with several structures or a composition at different physical conditions, are strongly encouraged -- that is, in order to extend this pilot study to more fullerene PNe, and to unveil the details of fullerene formation and of the potential carriers of the elusive UIR plateau features.
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