Fullerene Formation in the Planetary Nebula Tc1: Constraints from JWST Mid-Infrared Imaging

Abstract

We analyse mid-infrared imaging observations of the planetary nebula Tc 1 obtained with the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope, with the aim of constraining the spatial distribution and formation conditions of fullerene molecules (C60). The data reveal a non spherical nebular morphology characterized by concentric shells, filamentary structures, and a pronounced asymmetric feature. The emission attributed to C60 is not uniformly distributed, but is instead confined to localized regions within the nebula. Using the wavelength dependence of the observed emission, we estimate that the fullerene-rich regions correspond to intermediate dust temperatures in the range T ∼ 200–350 K. This suggests that fullerene formation requires a restricted thermal environment, with sufficient energy to restructure carbonaceous material while avoiding destruction of the closed cage structure.

The spatial confinement of the emission further indicates that local physical conditions, including radiation field intensity and shock-driven processing, play a dominant role. We interpret these results within a curvature-driven framework in which fullerenes form through the transformation of quasi-planar carbon networks.

The introduction of pentagonal defects into a hexagonal lattice induces positive curvature, leading to the formation of stable closed cages. The JWST observations of Tc 1 are consistent with this mechanism, linking the molecular structure of C60 to the dynamical and thermal properties of the nebula. These findings provide observational constraints on fullerene formation in evolved stellar environments and highlight the role of localized processes in governing complex carbon chemistry.