Gemini observations of Wolf-Rayet stars in the Local Group starburst galaxy IC 10^*

¹ Dept of Physics and Astronomy, University College London, Gower St, London WC1E 6BT, UK
² Département de Physique, Université Laval, and Observatoire du Mont Mégantic, Québec QC G1K 7P4, Canada
³ Institut d'Astrophysique, Université de Liège, 5 av. de Cointe, 4000 Liège, Belgium
⁴ K.U. Leuven, Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium
⁵ Institute of Astronomy, University of Cambridge, Madingley Road, CB3 OHA, UK

Corresponding author: P. A. Crowther, pac@star.ucl.ac.uk

Received: 2 January 2003
Accepted: 31 March 2003

Abstract

We present Gemini-N GMOS and CFHT MOS spectroscopy of Wolf-Rayet candidates in the Local Group dwarf galaxy IC 10 that were previously identified by Massey et al. and Royer et al. From the present spectroscopic survey, the WC/WN ratio for IC 10 remains unusually high, given its low metallicity, although none of the WC9 stars suspected from narrow-band imaging are confirmed. Our spectroscopy confirms 9 newly discovered Wolf-Rayet candidates from Royer et al., whilst spectral types of 14 Wolf-Rayet stars previously observed by Massey & Armandroff are refined here. In total, there are 26 spectroscopically confirmed Wolf-Rayet stars in IC 10. All but one of the fourteen WC stars are WC4–6 stars, the exception being # 10 from Massey et al., a broad-lined, apparently single WC7 star. There are a total of eleven WN stars, which are predominantly early WN3–4 stars, but include a rare WN10 star, #8 from Royer et al. #5 from Massey et al. is newly identified as a transition WN/C star. Consequently, the WC/WN ratio for IC10 is 14/11~1.3, unusually high for a metal-poor galaxy. Re-evaluating recent photometric data of Massey & Holmes, we suggest that the true WC/WN ratio may not be as low as ~0.3. Finally, we present ground-based finding charts for all confirmed WR stars, plus HST/WFPC2 charts for twelve cases.