2009ApJ...700.1988M

Large organic molecules and carbon clusters are basic building blocks of life, but their existence in the universe has not been confirmed beyond doubt. A number of unidentified absorption features (arising in the diffuse interstellar medium), usually called "Diffuse Interstellar Bands" (DIBs), are hypothesized to be produced by large molecules. Among these, buckminsterfullerene C₆₀ has gained much attention as a candidate for DIB absorbers because of its high stability in space. Two DIBs at λ ∼ 9577 Å and 9632 Å have been reported as possible features of C⁺₆₀. However, it is still not clear how their existence depends on their environment. We obtained high-resolution spectra of three stars in/around the Orion Nebula, to search for any correlations of the DIB strength with carrier's physical conditions, such as dust abundance and UV radiation field. We find three DIBs at λ ∼ 9017 Å, 9210 Å, and 9258 Å as additional C⁺₆₀ feature candidates, which could support this identification. These DIBs have asymmetric profiles similar to the longer wavelength features. However, we also find that the relative strengths of DIBs are close to unity and differ from laboratory measurements, a similar trend as noticed for the 9577/9632 DIBs.