Diffuse interstellar bands in (proto-) fullerene-rich environments

TL;DR

This study investigates the relationship between fullerenes and diffuse interstellar bands in planetary nebulae and R Coronae Borealis stars, revealing distinct spectral features and potential links to larger fullerenes and circumstellar molecules.

Contribution

First detailed optical spectral analysis of fullerene-rich environments exploring the connection between fullerenes and DIBs, identifying new features and potential molecular carriers.

Findings

Unusual strength of specific DIBs in different objects.

Detection of new broad features at 4000 A and 6525 A.

Possible link between DIBs and larger fullerenes or buckyonions.

Abstract

The recent infrared detection of fullerenes (C60 and C70) in Planetary Nebulae (PNe) and R Coronae Borealis (RCB) stars offers a beautiful opportunity for studying the diffuse interstellar bands (DIBs) in sources where fullerenes are abundant. Here we present for the first time a detailed inspection of the optical spectra of the hot RCB star DY Cen and two fullerene PNe (Tc 1 and M 1-20), which permits us to directly explore the fullerenes - DIB connection. The DIB spectrum of DY Cen (Garcia-Hernandez et al. 2012a) is remarkably different from that in fullerene PNe (Garcia-Hernandez & Diaz-Luis 2013). In particular, Tc 1 displays unusually strong 4428 A and 6309 A DIBs, which are normal (or not seen) in DY Cen. On the other hand, DY Cen displays an unusually strong 6284 A DIB that is found to be normal in fullerene PNe. We also report the detection of new broad and unidentified features centered at 4000 A and 6525 A in DY Cen and Tc 1, respectively. We suggest that the new 4000 A band seen in DY Cen may be related to the circumstellar proto-fullerenes seen at infrared wavelengths (Garcia-Hernandez et al. 2012a). However, the intense 4428 A DIB (probably also the 6309 A DIB and the new 6525 A band) may be related to the presence of larger fullerenes (e.g., C80, C240, C320, and C540) and buckyonions (multishell fullerenes such as C60@C240 and C60@C240@C540) in the circumstellar envelope of Tc 1 (Garcia-Hernandez & Diaz-Luis 2013).