The neon abundance in WC stars — I. ISO SWS spectroscopy of WR146 (WC6+O)⋆ Free

We present infrared spectroscopy in the wavelength range 2.6–20 μm of the WC6+0 binary system WR146 (MR112) obtained with the Short Wavelength Spectrometer (SWS) on the Infrared Space Observatory (ISO). These data are combined with ground-based optical (INT) and near-IR (UKIRT) spectroscopy and theoretical continuum distributions revealing E(B — V) = 2.8 mag, a continuum optical light ratio (WR:O) = 1:2 ± 1, a probable O8.5V companion and a distance of 750 pc. We obtain C/He=0.15 by number for the WC6 star from an analysis of near-IR recombination lines, a factor of 2 higher than previously estimated by Eenens & Williams. We find a WC6 terminal wind velocity of 2700 km s⁻¹ from the observed [Ne iii] 15.5-μm profile, while results from test WCE model atmospheric calculations and radio flux measurements imply M = 2.6 × 10⁻⁵ M_⊙ yr⁻¹. An analysis of the [Ne iii] 15.5-μm line yields a lower limit to the neon abundance of Ne/He = 3.4 × 10⁻³ by number. Our ISO spectra show no wind emission in either [Ne ii] 12.81 μm or [Ne v] 14.32 μm from which we estimate Ne iv/Ne iii ≤ 1. The resulting bound on the neon abundance in the WC6 star is thus 3.4 × 10⁻³ ≤ Ne/He ≤ 6.8 × 10⁻³. This result is in close accord with the predicted value of Ne/ He ∼ 6 × 10⁻3; from stellar evolution models of WC stars, during which the products of interior nuclear burning are revealed at the stellar surface.