1995A&A...295..171K

We present an analysis of the WO3 star, DR 1, which is located in the dwarf irregular galaxy IC 1613, and is surrounded by an HII region which shows nebular HeII 4686 A in emission, a rare phenomenon in nebulae surrounding Wolf-Rayet stars. We have derived E(B-V)=0.07 via a comparison of the observed Balmer line ratios to those predicted by theory, using the electron temperature of T_e=17100K derived from our nebular analysis. We find O/H=4.99x10^–5 by number for the nebula, in agreement with the O/H ratios found for other emission-line regions in IC 1613. We derive the following nebular mass fractions: X=0.761, Y=0.238 and Z=0.00091. After allowance for the contribution by the nebular continuum, we have derived a stellar absolute magnitude of M_V=-3.6 for DR 1, a stellar effective temperature of T_*=75000K via a HI and HeII Zanstra analysis, and a stellar luminosity of 10⁶L_☉. A terminal wind velocity of v_∞=2850km/s is derived for DR 1 from the width of the strongest stellar emission lines. We also performed an abundance analysis of the stellar wind via a recombination theory analysis of the stellar emission-line features, and derive X(C)=0.48, X(O)=0.27 and X(He)=0.25. These values are within the range found for other WO stars by Kingsburgh et al. (1994MNRAS.271..257K) and agree with those predicted by the Z=0.004 massive star evolutionary models of Meynet et al. (1994A&AS..103...97M), but not with their Z=0.001 models. Our observations confirm the prediction that WO stars in low-metallicity galaxies should be much more luminous than their counterparts in higher metallicity galaxies.