2012MNRAS.420.2785I

We have obtained high-resolution optical spectroscopy of 10 reddened O-type stars with Ultraviolet and Visual Echelle Spectrograph at Very Large Telescope to search for interstellar bands of the naphthalene cation (C₁₀H₈⁺) in the intervening clouds. No absorption features were detected near the laboratory strongest band of this cation at 6707 Å except for star HD 125241 (O9 I). Additional bands in the optical spectrum of this star appear to be consistent with other transitions of this cation. Under the assumption that the bands are caused by naphthalene cations, we derive a column density N_Np+ = (1.2±0.3) {x} 10 ¹³/cm2 similar to the column density claimed in the Perseus complex star Cernis 52. The strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797 Å suggests the presence of a σ-type cloud in the line of sight of HD 125241.