Fullerenes and fullerene-related molecules have been proposed as explanations for unidentified astronomical features such as the intense UV absorption band at 217 nm and the enigmatic diffuse interstellar bands (DIBs), In order to shed light on the a long-standing DIB’s problem, we search high-resolution and high-quality VLT/UVES optical spectra of the hot R Coronae Borealis (RCB) star DY Cen for electronic transitions of the neutral C60 fullerene molecule and DIBs. We report the non-detection of the strongest C60 electronic transitions (e.g., those at ∼376, 398, and 402 nm). DIBs towards DY Cen are normal for its reddening; the only exception is the DIB at 628 nm (possibly also the 722 nm DIB) that is found to be unusually strong. We also report the detection of a new broad (FWHM∼2 Å) and unidentified feature centered at∼400 nm. The non detection of neutral C60 in the high-quality VLT/UVES DY Cen’s spectrum may support recent experimental work, showing that the∼7.0, 8.5, 17.4, and 18.8 micron IR features seen in sources with polycyclic aromatic hydrocarbon (PAH)-like dominated spectra have to attributed to proto-fullerenes rather than to neutral C60. In addition, the new 400 nm DIB reported here (possibly also the carriers of the classical 628 nm and 722 nm DIBs) may be related to fullerene precursors; an organic compound containing pentagonal rings. These pentagonal carbon rings are usually present in hydrogenated amorphous carbon (HAC) nanoparticles and nanotubes, suggesting that they may be intimately related with the formation process of fullerenes.
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It is well known that fullerenes – big, complex, and highly resistant carbon molecules with potential applications in nanotechnology – are mostly seen in planetary nebulae (PNe); old dying stars with progenitor masses similar to our Sun. Fullerenes, like C60 and C70, have been detected in PNe whose infrared (IR) spectra are dominated by broad unidentified IR (UIR) plateau emissions. The identification of the chemical species (structure and composition) responsible for such UIR emission widely present in the Universe is a mystery in astrochemistry; although they are believed to be carbon-rich
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Accretion disks around compact objects are expected to enter an unstable phase at high luminosity. One instability may occur when the radiation pressure generated by accretion modifies the disk viscosity, resulting in the cyclic depletion and refilling of the inner disk on short timescales. Such a scenario, however, has only been quantitatively verified for a single stellar-mass black hole. Although there are hints of these cycles in a few isolated cases, their apparent absence in the variable emission of most bright accreting neutron stars and black holes has been a continuing puzzle. Here
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