HIGH-RESOLUTION OPTICAL SPECTROSCOPY OF DY Cen: DIFFUSE INTERSTELLAR BANDS IN A PROTO-FULLERENE CIRCUMSTELLAR ENVIRONMENT?

We search high-resolution and high-quality VLT/UVES optical spectra of the hot R Coronae Borealis star DY Cen for electronic transitions of the C60 molecule and diffuse interstellar bands (DIBs). We report the non-detection of the strongest C60 electronic transitions (e.g., those at ∼3760, 3980, and 4024 Å). The absence of C60 absorption bands may support recent laboratory results, which show that the ∼7.0, 8.5, 17.4, and 18.8 μm emission features seen in DY Cen—and other similar objects with polycyclic-aromatic-hydrocarbon-like dominated IR spectra—are attributable to proto-fullerenes or fullerene precursors rather than to C60. DIBs toward DY Cen are normal for its reddening; the only exception is the DIB at 6284 Å (possibly also the 7223 Å DIB) which is found to be unusually strong. We also report the detection of a new broad (FWHM ∼ 2 Å) and unidentified feature centered at ∼4000 Å. We suggest that this new band may be related to the circumstellar proto-fullerenes seen at infrared wavelengths.