A Mid-Infrared Spectral Survey of Galactic Wolf-Rayet Stars

Abstract

We present 8–13 μm spectra at resolution R ~ 600 of 29 northern Galactic Wolf-Rayet stars, including the first ever reported mid-infrared (MIR) spectrum for many. Among the subtypes of the stars studied were 14 WC, 13 WN, 1 WN/WC, and an additional reclassified WN. Lines of He I and He II, along with fine-structure lines of Ne II and S IV, are strongly present in 22 of the sources observed, while six of the sources exhibit the powerful emission of heated circumstellar carbon dust. We point out similarities between our spectra and Infrared Space Observatory (ISO) observations of several of the same sources and note an unresolved discrepancy between the two data sets for the WC6 star WR 146. We investigate the diagnostic power of MIR He I and He II lines for subtype discrimination and find the line ratio W_λ(9.7 μm He II)/W_λ(11.3 μm He I+He II) can provide moderate discrimination within the WN and WC types, though the small number of stars with corresponding line pairs detected made such assessment difficult.