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Issue A&A
Volume 419, Number 2, May IV 2004
Page(s) L17 - L20
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040128



A&A 419, L17-L20 (2004)
DOI: 10.1051/0004-6361:20040128

Letter

An exceptional population of late-type WC stars in the metal-rich spiral galaxy M 83

P. A. Crowther1, L. J. Hadfield1, H. Schild2 and W. Schmutz3

1  Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Rd, Shefffield, S3 7RH, UK
2  Institut für Astronomie, ETH-Zentrum, 8092 Zürich, Switzerland
3  Physikalisch-Meteorologisches Observatorium, 7260 Davos, Switzerland

(Received 27 February 2004 / Accepted 4 April 2004)

Abstract
We have surveyed the metal-rich spiral galaxy M 83 (NGC 5236) for its Wolf-Rayet population using VLT-FORS2 narrow-band imaging and follow-up spectroscopy. From a total of 280 candidates identified using He II $\lambda$4686 imaging, Multi Object Spectroscopy of 198 sources was carried out, revealing 132 objects containing bona-fide Wolf-Rayet features. From this sample, an exceptional W-R content of ~1030 is inferred, with N(WC)/ N(WN) ~ 1.3, continuing the trend to larger values at higher metallicity amongst Local Group galaxies. More dramatic is the dominance of late-type WC stars in M 83 with N(WC8-9)/ N(WC4-7) = 9 which we attribute to the sensitivity of the classification line C III $\lambda$5696 to mass-loss, providing the strength of WC winds scale with metallicity. One young massive compact cluster, #74 in our catalogue, hosts 20% of the entire galactic population, namely ~180 late WC stars and ~50 late WN stars.


Key words: galaxies: individual: M 83 -- stars: Wolf-Rayet

Offprint request: P. A. Crowther, Paul.Crowther@sheffield.ac.uk

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© ESO 2004


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