在红色矩形中搜索corannulene（C20H10）
Search for corannulene (C20H10) in the Red Rectangle
摘要：
多环芳烃（PAHs）被广泛接受为芳香族红外波段（AIB）的载体，但任何特定的星际PAH仍然缺乏明确的识别。对于极性多环芳烃，纯转动跃迁可以作为指纹进行识别。结合专门的实验，详细的模拟和观察，我们探索了mm域搜索特定的旋转跃迁corannulene（C20 H10）。我们对紫外光激发的C20 H10在红矩形环境中的发射光谱进行了高分辨光谱测量和模拟，计算了它的合成转动光谱。基于这些结果，我们在IRAM 30米望远镜上对这个源进行了第一次观测活动，以寻找（C20 H10）的几个高J旋转跃迁。对corannulene的J = 112 <-111跃迁的实验室检测表明，在这条谱线上不存在离心分裂。使用IRAM 30米望远镜对红矩形的观测没有显示任何观测频率的corannulene发射，对于J =135 -> 134跃迁，在137.615 GHz下的均方根噪声水平为Tmb = 8 mK。将噪声水平与合成光谱进行比较，我们能够估计相对于多环芳烃中碳的总丰度，锁定在corannulene中的碳的分数的上限约为1.0x10（-5）。灵敏度的实现表明，无线电光谱可以是一个强大的工具来寻找极性多环芳烃。我们比较了这个上限与模型的多环芳烃的大小分布，强调小的多环芳烃比预测的要少得多。我们表明，这不能解释的破坏，但更有可能与它们的形成在红色矩形的环境中的化学。
英文摘要：
Polycyclic Aromatic Hydrocarbons (PAHs) are widely accepted as the carriers of the Aromatic Infrared Bands (AIBs), but an unambiguous identification of any specific interstellar PAH is still missing. For polar PAHs, pure rotational transitions can be used as fingerprints for identification. Combining dedicated experiments, detailed simulations and observations, we explored the mm domain to search for specific rotational transitions of corannulene (C20H10). We performed high-resolution spectroscopic measurements and a simulation of the emission spectrum of UV-excited C20H10 in the environment of the Red Rectangle, calculating its synthetic rotational spectrum. Based on these results, we conducted a first observational campaign at the IRAM 30m telescope towards this source to search for several high-J rotational transitions of (C20H10). The laboratory detection of the J = 112 <- 111 transition of corannulene showed that no centrifugal splitting is present up to this line. Observations with the IRAM 30m telescope towards the Red Rectangle do not show any corannulene emission at any of the observed frequencies, down to a rms noise level of Tmb = 8 mK for the J =135 -> 134 transition at 137.615 GHz. Comparing the noise level with the synthetic spectrum, we are able to estimate an upper limit to the fraction of carbon locked in corannulene of about 1.0x10(-5) relative to the total abundance of carbon in PAHs. The sensitivity achieved shows that radio spectroscopy can be a powerful tool to search for polar PAHs. We compare this upper limit with models for the PAH size distribution, emphasising that small PAHs are much less abundant than predicted. We show that this cannot be explained by destruction but is more likely related to the chemistry of their formation in the environment of the Red Rectangle.
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