2016A&A...589A...5D

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 2.9-4.1µm 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 ∼3.4-3.6µm in both PNe. We conclude that if fulleranes are present in the fullerene-containing circumstellar environments of these PNe, then they seem to be much 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.