DR-1 - A WO3 STAR IN IC-1613 AND ITS SURROUNDING NEBULA, S3

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 H II region wh ich shows nebular He II 4686 Angstrom in emission, a rare phenomenon i n 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 = 17100 K derived fr om our nebular analysis. We find O/H = 4.99 x 10(-5) by number for the nebula, in agreement with the O/H ratios found for other emission-lin e 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 contribu tion by the nebular continuum, we have derived a stellar absolute magn itude of M(V) = -3.6 for DR 1, a stellar effective temperature of T = 75000 K via a H I and He II Zanstra analysis, and a stellar luminosit y of 10(6) L.. A terminal wind velocity of v(infinity) = 2850 km sec(- 1) is derived for DR 1 from the width of the strongest stellar emissio n lines. We also performed an abundance analysis of the stellar wind v ia a recombination theory analysis of the stellar emission-line featur es, 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. (1 994) and agree with those predicted by the Z = 0.004 massive star evol utionary models of Meynet et al. (1994), but not with their Z = 0.001 models. Our observations confirm the prediction that WO stars in low-m etallicity galaxies should be much more luminous than their counterpar ts in higher metallicity galaxies.