First evidence of the possible detection of diffuse circumstellar bands in AGB descendants

Abstract

The short transition phase between asymptotic giant branch stars (AGB; when circumstellar envelopes rich in small organic molecules are efficiently created) and planetary nebulae (PNe) represents a most active phase of molecular synthesis. Different complex organic molecules - e.g., polycyclic aromatic hydrocarbons and fullerenes - have been proposed as carriers of the enigmatic diffuse interstellar bands (DIBs). If the DIBs arise from such large carbon-based molecules, then they are also expected to be present in the circumstellar shells around C-rich AGB descendants; i.e., post-AGB stars and young PNe. Diffuse circumstellar bands (DCBs) in absorption have been unsuccessfully search for more than 40 years; the main difficulty being to distinguish the DCBs from the DIBs. Here we present a detailed DIB radial velocity analysis and a complete search of diffuse bands towards three young PNe (Tc 1, M 1-20, and IC 418) containing fullerenes. Interestingly, we report the first possible detection of two DCBs at 4428 and 5780 Å in the fullerene-rich circumstellar environment around PN Tc 1. This possible detection of DCBs in an environment rich in fullerenes and fullerene-related molecules could provide a link between fullerene compounds and some of the DIB carriers.