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Astron. Astrophys. 350, 1007-1017 (1999)


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Wolf-Rayet nebulae as tracers of stellar ionizing fluxes

I. M1-67

Paul A. Crowther 1, A. Pasquali 2, Orsola De Marco 1,3, W. Schmutz 3,4, D.J. Hillier 5 and A. de Koter 6

1 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
2 ST-ECF/ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
3 Institut für Astronomie, ETH-Zentrum, 8092 Zürich, Switzerland
4 Physikalisch-Meteorologisches Observatorium Davos, 7260 Davos Dorf, Switzerland
5 Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260, USA
6 Astronomical Institute `Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Received 2 June 1999 / Accepted 25 August 1999

Abstract

We use WR124 (WN8h) and its associated nebula M1-67, to test theoretical non-LTE models for Wolf-Rayet (WR) stars. Lyman continuum ionizing flux distributions derived from a stellar analysis of WR124, are compared with nebular properties via photo-ionization modelling. Our study demonstrates the significant role that line blanketing plays in affecting the Lyman ionizing energy distribution of WR stars, of particular relevance to the study of H II regions containing young stellar populations.

We confirm previous results that non-line blanketed WR energy distributions fail to explain the observed nebular properties of M1-67, such that the predicted ionizing spectrum is too hard. A line blanketed analysis of WR124 is carried out using the method of Hillier & Miller (1998), with stellar properties in accord with previous results, except that the inclusion of clumping in the stellar wind reduces its wind performance factor to only [FORMULA]2. The ionizing spectrum of the line blanketed model is much softer than for a comparable temperature unblanketed case, such that negligible flux is emitted with energy above the He I [FORMULA]504 edge. Photo-ionization modelling, incorporating the observed radial density distribution for M1-67 reveals excellent agreement with the observed nebular electron temperature, ionization balance and line strengths. An alternative stellar model of WR124 is calculated, following the technique of de Koter et al. (1997), augmented to include line blanketing following Schmutz et al. (1991). Good consistency is reached regarding the stellar properties of WR124, but agreement with the nebular properties of M1-67 is somewhat poorer than for the Hillier & Miller code.

Key words: stars: fundamental parameters – stars: individual: WR124 – stars: Wolf-Rayet – ISM: H ii regions – ISM: individual objects: M1-67

Send offprint requests to: P.A. Crowther (pac@star.ucl.ac.uk)

© European Southern Observatory (ESO) 1999

Online publication: October 14, 1999

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