2010MNRAS.407.2157I

We report the discovery of a new broad interstellar (or circumstellar) band at 7088.8±2.0 Å coincident to within the measurement uncertainties with the strongest band of the anthracene cation (C₁₄H₁₀⁺) as measured in gas-phase laboratory spectroscopy at low temperatures. The band is detected in the line of sight of star Cernis 52, a likely member of the very young star cluster IC 348, and is probably associated with cold absorbing material in an intervening molecular cloud of the Perseus star-forming region where various experiments have recently detected anomalous microwave emission. From the measured intensity and available oscillator strength we find a column density of implying that ∼0.008 per cent of the carbon in the cloud could be in the form of C₁₄H₁₀⁺. A similar abundance has been recently claimed for the naphthalene cation in this cloud. This is the first location outside the Solar system where specific polycyclic aromatic hydrocarbons (PAHs) are identified. We report observations of interstellar lines of CH and CH⁺ that support a rather high column density for these species and for molecular hydrogen. The strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797 Å suggests the presence of a `zeta'-type cloud in the line of sight (consistent with steep far-ultraviolet extinction and high molecular content). The presence of PAH cations and other related hydrogenated carbon molecules which are likely to occur in this type of clouds reinforces the suggestion that electric dipole radiation from fast-spinning PAHs is responsible of the anomalous microwave emission detected towards Perseus.