SIMBAD references

New Technology Telescope (NTT)/Son of Isaac (SOFI) imaging and spectroscopy of the Wolf-Rayet population in the massive cluster Westerlund 1 are presented. Narrow-band near-infrared (IR) imaging together with follow up spectroscopy reveals four new Wolf-Rayet stars, of which three were independently identified recently by Groh et al., bringing the confirmed Wolf-Rayet content to 24 (23 excluding source S) - representing 8 per cent of the known Galactic Wolf-Rayet population - comprising eight WC stars and 16 (15) WN stars. Revised coordinates and near-IR photometry are presented, whilst a quantitative near-IR spectral classification scheme for Wolf-Rayet stars is presented and applied to members of Westerlund 1. Late subtypes are dominant, with no subtypes earlier than WN5 or WC8 for the nitrogen and carbon sequences, respectively. A qualitative inspection of the WN stars suggests that most (∼75 per cent) are highly H deficient. The Wolf-Rayet binary fraction is high (≥62 per cent), on the basis of dust emission from WC stars, in addition to a significant WN binary fraction from hard X-ray detections according to Clark et al. We exploit the large WN population of Westerlund 1 to reassess its distance (∼5.0kpc) and extinction (A_KS∼ 0.96mag), such that it is located at the edge of the Galactic bar, with an oxygen metallicity ∼60 per cent higher than Orion. The observed ratio of WR stars to red and yellow hypergiants, N(WR)/N(RSG + YHG) ∼3, favours an age of ∼4.5-5.0Myr, with individual Wolf-Rayet stars descended from progenitors of initial mass ∼40-55M_☉. Qualitative estimates of current masses for non-dusty, H-free WR stars are presented, revealing 10-18M_☉, such that ∼75 per cent of the initial stellar mass has been removed via stellar winds or close binary evolution. We present a revision to the cluster turn-off mass for other Milky Way clusters in which Wolf-Rayet stars are known, based upon the latest temperature calibration for OB stars. Finally, comparisons between the observed WR population and subtype distribution in Westerlund 1 and instantaneous burst evolutionary synthesis models are presented.