The neon abundance in WC stars - I. ISO SWS spectroscopy of WR146 (WC6+O)
Crowther, P. A.; Willis, A. J.; Morris, P. W.; van der Hucht, K. A.; Conti, P. S.; Dessart, Luc; Maeder, A.
United Kingdom, Spain, Switzerland, United States, Netherlands
Abstract
We present infrared spectroscopy in the wavelength range 2.6-20mum of the WC6+O 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) = 2.8mag, 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 2700kms^-1 from the observed [Neiii] 15.5-μm profile, while results from test WCE model atmospheric calculations and radio flux measurements imply M = 2.6 x 10^ - 5M / yr^-1. An analysis of the [Neiii] 15.5-μm line yields a lower limit to the neon abundance of Ne/He=3.4x10^-3 by number. Our ISO spectra show no wind emission in either [Neii] 12.81 μm or [Nev] 14.32 μm from which we estimate Neiv/Neiii <= 1. The resulting bound on the neon abundance in the WC6 star is thus 3.4x10^-3<=Ne/He <=6.8x10^-3. This result is in close accord with the predicted value of Ne/He~6x10^-3 from stellar evolution models of WC stars, during which the products of interior nuclear burning are revealed at the stellar surface.