A search for naphthalene in diffuse interstellar clouds

TL;DR

This study used high-resolution optical spectroscopy of 10 reddened O-type stars to search for naphthalene cation features in interstellar clouds, detecting potential signals in one star and estimating its column density.

Contribution

First search for naphthalene cation in diffuse interstellar clouds using high-resolution spectroscopy, identifying possible presence in one star and estimating its abundance.

Findings

No detection of naphthalene cation in most stars

Possible detection in star HD 125241 with estimated column density

Evidence of a sigma-type cloud along the line of sight

Abstract

We have obtained high resolution optical spectroscopy of 10 reddened O-type stars with UVES at VLT to search for interstellar bands of the naphthalene cation (C$_{10}$H$_{8}$$^+$) in the intervening clouds. No absorption features were detected near the laboratory strongest band of this cation at 6707 \AA except for star HD 125241 (O9 I). Additional bands in the optical spectrum of this star appear to be consistent with other transitions of this cation. Under the assumption that the bands are caused by naphthalene cations we derive a column density N$_{Np^+}$ = (1.2$\pm$ 0.3) x 10 $^{13}$ cm$^{-2}$ similar to the column density claimed in the Perseus complex star Cernis 52 (Iglesias-Groth et al. 2008). The strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797 \AA suggests the presence of a $\sigma$-type cloud in the line of sight of HD 125241.