Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...295..171k&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 295, no. 1, p. 171-182
Astronomy and Astrophysics
Astrophysics
36
Abundance, Dwarf Galaxies, H Ii Regions, Irregular Galaxies, Stellar Winds, Wolf-Rayet Stars, Balmer Series, Electron Energy, Emission Spectra, Interstellar Matter, Stellar Temperature, Wind Velocity
Scientific paper
We present an analysis of the WO3 star, DR 1, which is located in the dwarf irregular galaxy IC 1613, and is surrounded by a H II region which shows nebular He II 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 Te = 17100 K derived from 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-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 MV = -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 luminosity of 106 solar luminosity. A terminal wind velocity of vinfinity = 2850 km/sec 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. (1994) and agree with those predicted by the Z = 0.004 massive star evolutionary models of Meyet et al. (1994), 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.
Barlow Michael J.
Kingsburgh Robin L.
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