A search for diffuse bands in fullerene planetary nebulae: evidence of diffuse circumstellar bands

TL;DR

This study investigates diffuse interstellar bands in fullerene-rich planetary nebulae, finding evidence of diffuse circumstellar bands potentially linked to fullerenes, and highlights the unique spectral features associated with these environments.

Contribution

It presents the first tentative detection of diffuse circumstellar bands in fullerene-rich planetary nebulae, suggesting a possible connection between fullerenes and DIB carriers.

Findings

Unusually strong 4428 Å absorption in fullerene PNe

Tentative detection of DCBs at 4428 and 5780 Å in Tc 1

Absence of neutral C60 optical bands in IC 418

Abstract

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 fullerene PNe. Similar to Tc 1, the strongest optical bands of neutral C60 are not detected towards IC 418. Our high-quality (S/N > 300) spectra for PN Tc 1, together with its large radial velocity, permit us to search for the presence of diffuse bands of circumstellar origin, which we refer to as diffuse circumstellar bands (DCBs). We report the first tentative detection of two DCBs at 4428 and 5780 A in the fullerene-rich circumstellar environment around the PN Tc 1. Laboratory and theoretical studies of fullerenes in their multifarious manifestations (carbon onions, fullerene clusters, or even complex species formed by fullerenes and other molecules like PAHs or metals) may help solve the mystery of some of the diffuse band carriers.