Wolf-Rayet stars in M33 - I. Optical spectroscopy using CFHT-MOS

Abstract

We have obtained spectroscopy of a large sample of Wolf-Rayet stars in M33 with the Canada-France-Hawaii Telescope Multi-Object Spectrograph (CFHT-MOS), including 26 WC stars, 15 WN stars and a WN/C star. In general, spectral types are merely refined, although the spectral type of X9 from Massey & Johnson is revised from WNL?+abs to WC4+abs, whilst their G1 and C21 candidates are not confirmed as Wolf-Rayet stars. We also re-examine the metallicity gradient of M33 from H ii regions and identify the present sample, lying in the inner disc, with 8.6 ≤ log(O/H) ≤ 8.9. Spectral types are in accord with similar regions in the Milky Way. Our large sample has allowed us to examine the claimed anticorrelation between WC linewidths and galactocentric distance by Schild et al. We find a much larger scatter, though there remains an absence of broad-line WC stars in the inner disc and narrow-line WC stars in the outer galaxy.