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VLT/FORS Surveys of Wolf-Rayet Stars in the Nearby Universe

Published online by Cambridge University Press:  01 December 2007

Lucy J. Hadfield  and
Paul A. Crowther
Lucy J. Hadfield
Affiliation:
Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA email: [email protected]
Paul A. Crowther
Affiliation:
Dept. of Physics & Astronomy, The University of Sheffield, The Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK email: [email protected]
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Abstract

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We present results from a series of VLT/FORS narrow-band imaging and spectroscopic surveys of Wolf-Rayet (WR) stars in nearby spiral galaxies and compare observed populations in high- and low metallicity environments. The metal-rich galaxy M 83 is seen to host an exceptional WR content, with over 1000 WR stars being detected. N(WC)/N(WN) ~ 1.2 and late-type WC subtypes dominate the WC population. At low metallicity, ~100 stars has been identified within NGC 1313, with N(WC)/N(WN) ~ 0.5. In contrast to M83, the WC population of NGC 1313 comprises solely early subtypes plus a WO star (the first WO star to be identified beyond the Local Group). Consequently, the dominant WC subtype may serve as a crude metallicity diagnostic for WR galaxies.

In addition, the WR content of the blue compact dwarf galaxy NGC 3125 is examined. Previous UV and optical spectroscopic studies of knot A in NGC 3125 derive WR populations which differ by more than an order of magnitude. New VLT observations and archival HST spectroscopy reconcile this discrepancy via the use of LMC WR spectral templates and a reduced nebular-derived interstellar extinction. Empirical N(WR)/N(O) ratios for clusters within NGC 3125 are a factor of two higher than evolutionary synthesis predictions but are consistent with those observed for other young massive clusters.

Keywords

stars: Wolf-Rayet – galaxies: individual (NGC 1313, M 83, NGC 3125) – galaxies: stellar content
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S250: Massive Stars as Cosmic Engines , December 2007 , pp. 327 - 332
Copyright
Copyright © International Astronomical Union 2008

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