The neon abundance in WC stars. II. ISO-SWS spectroscopy of WR 90 (HD 156385)

In general, observationally derived wind compositions of WR stars are in reasonable agreement with predictions from stellar evolution models for massive stars. However, Barlow et al. (1988) identified a major discrepancy for neon in ,2 Vel (WC8+0) using ground-based observations. The advent of the ESA Infrared Space Observatory (ISO) has allowed the study of neon in many more WC stars, using mid-IR fine structure lines ([Nell] 12.81 j-tm, [Nem] 15.55 j-tm and [Nev] 14.32 /-lm). Willis et al. (1998) used ISO-sws observations of WR 146 (WC5+0) to derive a neon abundance that was within the range expected theoretically. Here we undertake a study of WR90 (HD 156385), the only (apparently) single WC7 star in our Galaxy, using ISO-sws spectroscopy. The only spectroscopic neon feature in the mid-IR of WR 90 is [Nom] 15.55 usu, in addition to numerous C IV and He II transitions (see Figure 1).