Detections of C60 and C70 fullerenes in planetary nebulae (PNe) of the Magellanic Clouds and of our own Galaxy have raised the idea that other forms of carbon such as hydrogenated fullerenes (fulleranes like C60H36 and C60H18), buckyonions, and carbon nanotubes, may be widespread in the Universe. Here we present VLT/ISAAC spectra (R ~600) in the 2.9-4.1 microns spectral region for the Galactic PNe Tc 1 and M 1-20, which have been used to search for fullerene-based molecules in their fullerene-rich circumstellar environments. We report the non-detection of the most intense infrared bands of several fulleranes around ~3.4-3.6 microns in both PNe. We conclude that if fulleranes are present in the fullerene-containing circumstellar environments of these PNe, then they seem to be by far less abundant than C60 and C70. Our non-detections together with the (tentative) fulleranes detection in the proto-PN IRAS 01005+7910 suggest that fulleranes may be formed in the short transition phase between AGB stars and PNe but they are quickly destroyed by the UV radiation field from the central star.
Since the first laboratory synthesis of C$_{60}$ in 1985, fullerene-related species have been proposed to interpret various astronomical features. After more than 25 years' efforts, several circumstellar and interstellar features have been convincingly assigned to C$_{60}$, C$_{70}$, and C$_{60}^+$. These successes resulted from the recent advancements in observational, experimental, as well as computational techniques, and re-stimulated interest in searching for fullerene derivatives in space. As one of the most important fullerene derivatives, hydrogenated fullerene (fullerane) is likely to …
The recent detection of fullerene (C$_{60}$) in space and the positive assignment of five diffuse interstellar bands to C$_{60}^+$ reinforce the notion that fullerene-related compounds can be efficiently formed in circumstellar envelopes and be present in significant quantities in the interstellar medium. Experimental studies have shown that C$_{60}$ can be readily hydrogenated, raising the possibility that hydrogenated fullerenes (or fulleranes, C$_{60}$H$_m$, $m=1-60$) may be abundant in space. In this paper, we present theoretical studies of the vibrational modes of isomers of C$_{60}$H$_m$…
The main goal of this thesis is to unveil some questions related to the formation of complex fullerene-based molecules in space, with the aim of resolving some key problems in astrophysics. The unexpected detections of fullerenes and graphene (possible C24) in the H-rich circumstellar environments of evolved stars indicate that these complex molecules are not so rare and bring the idea that other forms of carbon such as hydrogenated fullerenes (fulleranes), buckyonions, and carbon nanotubes may be widespread in the Universe, being closely involved in many aspects of circumstellar/interstellar …
Large fullerenes and fullerene-based molecules have been proposed as carriers of diffuse interstellar bands (DIBs). The recent detection of the most common fullerenes (C60 and C70) around some planetary nebulae (PNe) now enable us to study the DIBs towards fullerene-rich space environments. We search DIBs in the optical spectra towards three fullerene-containing PNe (Tc 1, M 1-20, and IC 418). Special attention is given to DIBs which are found to be unusually intense towards these fullerene sources. In particular, an unusually strong 4428A absorption feature is a common charateristic of fuller…
Polycyclic aromatic hydrocarbons (PAHs) and fullerenes play a major role in the physics and chemistry of the interstellar medium. Based on a number of recent experimental and theoretical investigations we developed a model in which PAHs are subject to photo-dissociation (carbon and hydrogen loss) and hydrogenation. We take into account that dehydrogenated PAHs may fold into closed structures -- fullerenes. Fullerenes, in their turn, can be also hydrogenated, becoming fulleranes, and photo-dissociated, losing carbon and hydrogen atoms. The carbon loss leads to shrinking of fullerene cages to sm…
我们提出了一个研究16 PNe富勒烯已被发现在他们的斯皮策光谱。这个大样本的对象提供了一个独特的机会来测试条件下的富勒烯形成和生存在不同的金属环境，因为我们正在分析五个来源在我们自己的银河系，四个在LMC，和七个在SMC。在研究中的16个PNe中，我们首次检测到PN M 1-60中的C60（也可能是C70）富勒烯，以及PN K 3-54中不寻常的6.6，9.8和20 um特征（可能是平面C24）。虽然选择效应在原始样品中观察到的PNE与斯皮策可能会发挥潜在的重要作用的统计数据，我们发现，富勒烯的检测率在C丰富的PNE的金属含量降低（5%的银河系，20%的LMC，和44%的SMC）增加。云光电离模型将观测到的红外通量与中心恒星相匹配，这些恒星的有效温度范围相当窄（30，000 - 45，000 K），表明这些物体的共同进化状态和类似的富勒烯形成条件。在银河系源中观测到的C60强度比证实了我们先前在MC中的发现，即富勒烯发射不是由来自中心恒星的紫外辐射激发的。云模型还表明，线和风覆盖的模型大气可以通过光电离解释许多观测到的[NeIII]/[NeII]比率，这表明可能是来自中央恒星的紫外线辐射，而不是冲击，引发了星周尘埃颗粒的分解。手头的数据，我们建议，最有可能的解释形成的富勒烯和石墨烯前体在PNe是，这些分子物种是建立从光化学处理的含碳化合物的芳香族和脂肪族结构的混合物类似的HAC灰尘…
We present seeing-limited narrow-band mid-IR GTC/CanariCam images of the spatially extended fullerene-containing planetary nebula (PN) IC 418. The narrow-band images cover the C60 fullerene band at 17.4 μm, the polycyclic aromatic hydrocarbon like (PAH-like) feature at 11.3 μm, the broad 9-13 μm feature, and their adjacent continua at 9.8 and 20.5 μm. We study the relative spatial distribution of these complex species, all detected in the Spitzer and Infrared Space Observatory (ISO) spectra of IC 418, with the aim of getting observational constraints to the formation process of fullerenes in H…
Recent detections of C$_{60}$, C$_{70}$, and C$_{60}^+$ in space induced extensive studies of fullerene derivatives in circumstellar environments. As the promising fullerene sources, protoplanetary nebulae (PPNe) show a number of unidentified bands in their infrared spectra, among which a small sample exhibits an enigmatic feature at $\sim21$\,$μ$m. Hydrogenation of fullerenes can produce fulleranes emitting new infrared bands. In this paper, we investigate the possibility of fulleranes (C$_{60}$H$_m$) as the carrier of the 21\,$μ$m feature in terms of theoretical vibrational spectra of fuller…
Extra-galactic planetary nebulae (PNe) permit the study of dust and molecules in metallicity environments other than the Galaxy. Their known distances lower the number of free parameters in the observations vs. models comparison, providing strong constraints on the gas-phase and solid-state astrochemistry models. Observations of PNe in the Galaxy and other Local Group galaxies such as the Magellanic Clouds (MC) provide evidence that metallicity affects the production of dust as well as the formation of complex organic molecules and inorganic solid-state compounds in their circumstellar envelop…
The presence of neutral C60 fullerenes in circumstellar environments has been firmly established by astronomical observations as well as laboratory experiments and quantum-chemistry calculations. However, the large variations observed in the C60 17.4um/18.9um band ratios indicate that either additional emitters should contribute to the astronomical IR spectra or there exist unknown physical processes besides thermal and UV excitation. Fullerene-based molecules such as metallofullerenes and fullerene-adducts are natural candidate species as potential additional emitters, but no specific species…
Circumstellar envelopes (CEs) around evolved stars are an active site for the production of molecules. After evolving through the Asymptotic Giant Branch (AGB), proto-planetary nebula (PPN), to planetary nebula (PN) phases, CEs ultimately merge with the interstellar medium (ISM). The study of molecules in PNe, therefore, is essential to understanding the transition from stellar to interstellar materials. So far, over 20 molecular species have been discovered in PNe. The molecular composition of PNe is rather different from those of AGB and PPNe, suggesting that the molecules synthesized in PN …
Detection of unidentified molecular pure rotational lines in C-rich PNe I. The fullerene-containing PN IC 418
Instituto de Astrofísica de Canarias (IAC)（加那利天体物理研究所）；Universidad de La Laguna (ULL)（拉各鲁纳大学）；Instituto de Física Fundamental (IFF, CSIC)（基础物理研究所）；Observatorio Astronómico Nacional (OAN, IGN/CNIG)（国家天文台）；Universidad de Valladolid（巴利亚多利德大学）；Consejo Superior de Investigaciones Científicas (CSIC)（西班牙高等科学研究委员会）；Universitat de Barcelona (UB)（巴塞罗那大学）
The late stages of stellar evolution from asymptotic giant branch stars to planetary nebulae are now known to be an active phase of molecular synthesis. Over 80 gas-phase molecules have been detected through rotational transitions in the mm/submm region. Infrared spectroscopy has also detected inorganic minerals, fullerenes, and organic solids. The synthesis of these molecules and solids take place over very low density ($<10^6$ cm$^{-3}$) and short ($\sim10^3$ yr) time scales. The complex organics are observed to have mixed aromatic/aliphatic structures and may be related to the complex organ…
