Flux-calibrated spectrum of GR 290 (grey line) compared with the best-fit β = 2 CMFGEN model (black line). Measured photometric magnitudes and corresponding bandwidths are indicated. The model spectrum is scaled for the distance to the M 33 and the interstellar extinction (E_(B−V) =0.06) is applied to it. The adopted distance to M33 is 847±61 kpc (distance module 24.64±0.15) from Galleti et al. (2004).