The neon abundance in WC stars .1. ISO SWS spectroscopy of WR146 (WC6+O)

We present infrared spectroscopy in the wavelength range 2.6-20 mu m 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) = 2.8 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-LR 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 [Nem] 15.5-mu m profile, while results from test WCE model atmospheric calculations and radio flux measurements imply M = 2.6 x 10(-5) Mo yr(-1). An analysis of the [Ne mi 15.5-mu m line yields a lower limit to the neon abundance of Ne/He = 3.4 x 10(-3) by number. Our ISO spectra show no wind emission in either [Ne II] 12.81 mu m or [Ne v] 14.32 mu m from which we estimate Ne IV/Ne III less than or equal to 1. The resulting bound on the neon abundance in the WC6 star is thus 3.4 x 10(-3) less than or equal to Ne/He less than or equal to 6.8 x 10(-3). This result is in close accord with the predicted value of Ne/He similar to 6 x 10(-3) from stellar evolution models of WC stars, during which the products of interior nuclear burning are revealed at the stellar surface.